Is My Gaming PC Parts List Solid?

For your needs, 64GB RAM should be plenty, especially if you're running high-end games and multitasking. The motherboard options you mentioned, like the B850, are good choices. I’d also recommend checking the Montech PSU options, especially the 1200W—they provide great performance without breaking the bank.

The 9800X3D is generally preferred for gaming over the 9950X3D, so sticking with that should be fine. As for the GPU, the RTX 5090 is currently the best option available; the 4090 has been discontinued, so you won't find one in production anymore. Regarding RAM, DDR7 isn't a thing yet—go with 64GB DDR5 instead. This build deserves it, and you'll benefit from having more RAM. For power, a minimum of 1000W is advisable for the RTX 5090 since it pulls quite a bit of power.

You won’t regret going with the 5090; it outperforms the 4090. 850W might be cutting it close, so I'd steer you towards 1000W or more. You’re fine with 32GB, but if you want to future-proof or plan on heavy multitasking, bumping up to 64GB wouldn’t hurt. Stick with good quality components like the B850 motherboard; spending more usually doesn’t yield proportional benefits.

Definitely keep the 9800X3D for gaming; it’s more efficient for 4K performance compared to the 9950. For the motherboard, I'd say a B850 is solid, while an X870 is nice if you need fancy features. Also, avoid worrying about DDR7 since it isn't available yet—DDR5 is your best bet. And yes, with a 5090, I'd recommend going with a 1200W PSU just to give you some breathing room.