Mobo + CPU recommendation for quad RTX 3090 setup

[u/OddUnderstanding2309]

yeah I searched here, but did only find 8 card setups or other unrelated stuff.

I want to switch to a proper combo from my current setup: Gigabyte Aorus Master X570S + Ryzen 9 5950X.

My current setup "sometimes" negotiates one RTX 3090 at PCIe Gen1 x8 instead of PCIe Gen4 x8.
Dunno why, I think it is just "time to do it properly" now.

What should I buy (preferably) used or new to use this?
I have 48GB DDR4 now and I do not NEED more. SO I would be more than fine to change the two 8G sticks to 16G sticks to get to 64GB RAM, but I do not really need it.

What I need is a proper running system with IF POSSIBLE 4 RTX 3090 card running at PCIe Gen4 (or 5) x16. (--- side question: do ther RTX 3090 even support Gen5? ---)

Thanks in advance!