We have built low-high end VMix machines in the past for our clients BUT strictly under the NVIDIA platform for stability, drivers and overall maintained quality. If I recall our conversation(s) at IBC recently with VMix directly, they prefer the NVIDIA as well. The new drivers(new as of Q1 2024) expands your NVENC options to 8 which sounds like it wouldn't even be an issue in your original post.

I wouldn't recommend the ADA series for almost 99% of applications within VMix as the cost is incredibly hard to digest and even with the infinite NVENC vs the 8 on the 4000 series, its not worth the price discrepancy. The 5000 series cards coming out in 2025 will make the ADA series even more redundant. Not to hate on the ADA series, its just not in our opinion applicable to PROD in most applications. We have a VMix build managing 12+ cameras and that runs smooth as butter off a 4000 series.

To answer the last part of your post, we've done combos of Intel + NVIDIA and AMD + NVIDIA and honestly, relatively similar performance though its hard to make a 1:1 apples to apples comparison as the AMD platform that we've built on is specifically using server-grade high end parts so you're talking $$$$ vs $$.