Wow the timing, I spent a few hours trying to get my head around these three choices last night. Got to roughly similar conclusions. And I still don't know what to do.

I have more money than sense. I don't even know (yet) how silly it is, but maybe a Strix Halo, with 2x 5090s with p2p pcie patch? I'd do more 5090s but the power consumption and need to water cool is too much for me.

I'm also itchy because it seems like Ryzen Pro 495 is coming soon with even more unified RAM... (thoughts very much appreciate on any of this...)

AMD ROCm has come a long long long ways since last year, but you'll probably be happier not dealing with AMD's software.

I posted another comment with my experience with AMD 395+, I am overall happy and it's usable now, but it's only useful for models under 64gb of vram due to the active parameter counts on larger MoEs.

If you add 2x 5090s, do you actually need the base system?