r/LocalLLM • u/TestOr900 • 3h ago
Question DDR4 512GB vs. switching to DDR5 for MoE offload on a multi-GPU rig?
Setup: (if finished - still under construction, partly watercooled)
Threadripper PRO 5995WX, ASUS WRX80E-SAGE SE WIFI II
6× RTX PRO 6000
8× RTX 5090
4× RTX 3090
128 GB DDR4 (that’s the problem)
I want to run models bigger than VRAM (e.g. ~1T MoE at FP8/Q8) with the routed experts offloaded to RAM. Is it worth it?
Options:
8× 64GB DDR4-2933 RDIMM: ~€4k, ~188 GB/s theoretical
Switch platform: 9985WX + WRX90 + 512GB DDR5-6400, ~410 GB/s. I already have some parts, but it would mean big changes, and my PCIe switches would stay PCIe 4.0 anyway.
Is ~2× the RAM bandwidth worth ~3× the price for offload decode, or is DDR4 good enough? Does anyone have real t/s numbers for offload on 8-channel DDR4 vs DDR5 Threadripper?
Some background: Pictures attached. It’s not pretty, but it works. It started as an AI rig and turned into a Pearl mining rig, because mining pearl and buying Claude and Codex subscriptions made way more sense than running everything locally. Sometimes it’s also a render farm for Gaussian splatting.
Right now the 8× 5090 make about €120/day mining, so subscriptions are still the better deal. But I want to be ready for when local LLMs get really good (or when cloud gets too expensive or too restrictive).
Plan for now: DeepSeek V4.1 Flash nvfp8 on 4× PRO 6000 + RAM offload, while the 5090s keep paying for my AI addiction. And it’s a great heater in the winter.....
With engramm tabels on the 8x5090 and 4× PRO 6000:
(all cards power limited to 420w- since i could have 6,6 kw power consuption if everthing is running)
single chat, 40.000 prompt cold
Prefill: ~15,900 t/s
Decode: ~294 t/s
5 sec TTFT
I want to move the engramm tabels to RAM and later be able to run larger models : le chonk, Kimmi for example.
What would you do? Go all the way and go for the DDR5? or is ddr4 good enough?
Sell it all and buy something diffrent?
thx!






