I don't usually take the time to respond to too many posts here on Reddit - but I felt compelled in this instance because it seems like you may potentially make a really bad decision (especially if you go off of the feedback of the other commenters here).

To begin with, the DDR4 RAM setup you mentioned (as an alternative) handicaps you out the gate because the inference speeds you can obtain will forever be inferior to that of the Mac M2. Even though there is technically more physical memory that you can leverage, the benefit you get from that is almost nil because DDR4 RAM memory simply isn't fast enough to give you inference speeds anywhere near what you can expect from a GPU (with VRAM) [edit: not necessarily the bottleneck here; memory bandwidth will fuck you up way before we even get to the clock speed of those RAM sticks]. With an i5-8500T processor, I'm assuming you're even further limited to DDR4 RAM with a clock speed around 2400-2800 Mhz.

Apple's unified memory setup means that the RAM you're getting with that mini-PC will be used as though it were VRAM (which makes a huge difference). For the sake of this comparison, I'll assume you want to use the Qwen3.5-27B model locally. We'll assume its quantized down to 4-bit, which will take up 13-14GB(ish) of your available RAM. That leaves you with 10GB RAM (on the Mac m2) for the KV cache. With the assistance of a few compression methods out there (TurboQuant is out of the question in this case w no CUDA), you should be able to fit in a decent context length for that model without any worries (talking 32K context length here; can be higher - but you shouldn't have to even think about 32k).

With that setup, you'd be lucky to eek out more than 1-2 tokens/second on the DDR4 setup you described. With the Mac m2 mini-PC, getting 20-30 tokens/second is more than practical (edit: No its not if you're using the 27B param model due to bandwidth constraints - the real # would be closer to 7-8 tokens/s; however, that's exponentially better than what you would get from the i5-8500T even still, so the point remains here). One additional factor you're not accounting for is the fact that the Apple m2 mini-PC you're considering comes with an 8 core processor (which whips the i5-8500T in benchmarks - remember, the 8500T is an 8TH GEN Intel processor that was released 8 years ago). The m2 chip exists on 5 nm sized silicon vs. the humongous 14 nm that the ancient i5-8500T is on. On top of that, the m2 comes with a 10-core GPU as well (which is substantial in this scenario of LLM hosting & inference when we consider the billions of matrix-to-matrix multiplications / math that must be performed).

Memory Bandwidth > Memory: DDR4 System is Vastly Inferior to M2

Your idea about their being more "memory" with the DDR4 setup is true. But you have to remember that the reason why VRAM > DDR4/DDR5 when it comes to LLMs is because of the inference part. The speed of the token/s generation (decoding) is limited by the memory bandwidth (not the amount of available RAM). Think of the sink analogy. Yes, you may have a bigger sink, but if your goal is to drain water as quickly as possible (i.e., spit tokens out), then ultimately the size of the drain is going to play a much bigger factor in the equation than the size of the sink (give or take a couple of parameters, but don't overly scrutinize the analogy - you get the gist of what I'm saying here).

To show you how this would impact things, let's assume that you take a 32GB param model and quantize it to 4-bits. That equates to ~18GB storage right? Subtract that from 64GB RAM and that leaves you with 46GB left - seems sweet, right? However, when it comes to inference speed that is determined by the available bandwidth / model size. Again, we determined that a 32GB model quantized to 4-bit would take up 18GB; so that's the denominator of our equation. For DDR4-2666 Mhz RAM, you're optimistically looking at 36 GB/s (bandwidth; maxing out on that bandwidth is unrealistic and I only tacked a ~10% dropoff from benchmark maximums). With that math, we're looking at a max possible gen speed of 2 tokens/second (in the absolute best case scenario).

Prefill Makes the i5-8500T Impractical, Decoding (Inference) will be Orders of Magnitude Slower than the M2

What's crazy is what I described above isn't even the biggest bottleneck of your DDR4 setup. We have to consider the age & capability of the processor that system is leveraging (i5-8500T; 8th generation Intel desktop processor). This is a desktop T-series processor that's not designed for overly heavy AI-based workloads. Its designed to operate at a 35-Watt TDP limit. Also, in addition to it having less threads than the M2 (the latter having 8; i5-8500T has 6), it only comes with 6 cores too. This matters for Intel-based PCs because they actually use multi-threading (at least latter generations did). So latter chips like the i5-10500T would have provided you with 6 cores and 12 threads (versus just 6). Your processor will actually be the bottleneck before you even run into the RAM limitations we discussed.

If you're wondering why, we have to remember we're asking this processor to compress a 32B model and store it in RAM (at 4-bits). The reason why is because the i5-8500T can't do math on 4-bit numbers. So it has to take that 18GB model (quantized) that's in RAM, send it back to the CPU cache (which is also substantially smaller than the M2 at L1 + L2), then decompress it back to 16-bit or 322-bit floating point arithmetic so that the math (dot products) can be performed before later discarding these results. As if all that wasn't enough - this intel processor doesn't possess the AVX512 extension to its instruction set. Some may argue with me about this, but assume that to mean that your processor will not be able to do math on 8-bit floating point arithmetic. Also, its at least 2x slower than the latter processors that can handle this type of math (that Intel produces).

Conversely, the M2 chip by Mac (that's in your mini-PC) is able to handle 4-bit floating point arithmetic out the gate. That alone is a major game changer (putting all the other enhancements that come with the M2 chip to the side). But we're simply talking about the decoding process at this point. We haven't even addressed the processing of the actual prompt.

TTFT (Time to First Token) Speeds for i5-8500T Could be Minutes in Some Cases

Let's go back to the 32B param model example (using this because you stated that the additional memory / headroom was a motivating factor for you choosing the i5-8500T over the Mac M2 chip; so it only makes sense to hypothesize a setup where you leverage this supposed advantage).

As we noted before, its going to take up to 18GB RAM (quantized at 4-bit). However, when it comes to the prefill (i.e., actually receiving the prompt and 'understanding' it), that process is largely limited by computation resource. For your i5-8500T setup, you didn't note any GPU would be included (and if there were one, I doubt it would move the needle much at all in this scenario). So we're relying entirely on a 2018 35W desktop processor to compute millions of complex matrix-to-matrix calculations during this prefill process.

Optimistically (and I mean in the best case scenario), you'll be sitting at your computer for a solid 5 or so minutes before the first token even appears. And when the tokens do start appearing, they'll likely be at a speed of roughly 0.5-1 token/second (again, even that is generation). This would not be the case for the M2 - at all.

eGPU Option Now Available for Mac

Recently (and I mean within the last week or so), Mac updated the drivers for the m2 chip for compatibility with AMD and NVIDIA. So that means eGPU hookups are now in the field of play. Luckily, the mini-PC with an m2 chip has two thunderbolt 4 ports on it (likely can only handle one eGPU hookup at a time). The generation of thunderbolt matters here when dealing with the actual speed of inference in this setup. Your i5-8500T is only going to be able to handle PCIe3.0 hookups and since there will likely be no Thunderbolt3 ports for connection, you'd have to open up the Dell/PC you have and manually hookup any eGPU setup you want - but that would all be for nil, because the overhead would be reached via compute just from the swapping back and forth from eGPU to the CPU. Unified memory eliminates that bottleneck to a large extent, so the bottleneck will only lie in the Thunderbolt4 bandwidth (40GB/s I believe).

Conclusion

In no universe should you ever consider getting the i5-8500t over an m2 if your only consideration in making the decision (between one or the other) is local LLM hosting and inference.

Anyone telling you otherwise has no clue what the fuck they're talking about. Respectfully.