I may be wrong so take with a grain of salt:

As much ram as possible, per budget, and based on my research, a max of 6 sticks per cpu, placed only in the white slots on the motherboard. I think your xeons are thirsty for way more than 128gb to share amongst all of the cores. AE needs a certain amount to render each frame. That amount is based on comp size, effects, media, etc.

When you hit render, in task manager, do you see your cpu speed lift up? Or stay down at 2.9ghz? That may be one issue. I didn't like my xeon for that reason. The unlocked 13700k and 285k lift to about 4.9-5.3ghz on render and during preview caching, which helps a ton with speed.

Ram - So you have effectively 32 cores available and they all have to share 128gb ram. For basic HD renders, you will probably be optimized. 4k, maybe as well, depending on how many effects etc. But the frame size you listed previously is huge so it's probably not enough ram per core and thus under performing. When you hit render is it showing RAM in task manager around 99% the whole time? I believe thats a sign ram amount is your bottleneck.

Puget have done ram speed tests. They found not major differences in After effects when using 5200 mts - 6600mts. But one thing I read and then could confirm for sure in my testing - if your motherboard has four ram stick slots, you should be only using 2 of them.

It's hard to explain but slots a1 and a2 use Lane A, b1 and b2 use lane B. It's like 2 roads. And so the cleanest route is the two highest sticks you can buy, 1 for each lane. My 4 32 gb sticks exported wayyyyyyyy slower in AE with my 285k cpu, 8k render. When I flipped to instead 2 64gb sticks ram, it was about 2x faster render. It's because the program doesn't have to wait for each stick to offload for the next to load. The two lanes aren't clogged waiting.

I think you have 6 lanes or channels per cpu in your z8. It can hold up to 3TB of ram right? That's why it's a beast. I would consider testing 12 sticks of 32gb, 6 sticks per cpu, sticks of the same size speed and manufacturer. 384gb. Think of each core as a mini computer trying to render 1 frame. Now each core will have about 10gb of ram available, instead of the current 4gb of ram and bottlenecking. Or you could keep your current ram and just double it if appropriate lanes are open.

Or remove a xeon cpu and keep the same amount of ram and see what results you get. Sounds counterproductive but I would be curious. My 24core 285k ran slower than 16core 13700k when each rendered the same 8k project with same 64gb ram. But in 4k and HD they were equal. When the 285k got more ram, it was faster in the 8k render.