What is the best CPU to pair with an RTX 5090 for 4K gaming?

For your situation, I gotta be honest, I'd suggest sticking with a more budget-conscious approach like the AMD Ryzen 7 7800X3D Processor. Ngl, jumping on the hype train for the AMD Ryzen 9 9950X or the upcoming Arrow Lake chips right at launch is risky and pricey. In my experience, early bios issues and "early adopter tax" are basically a given.

At 4K, you're mostly GPU bound anyway, so spending an extra $200-300 on a CPU won't actually change your life. I've been there... spent too much on a flagship just to see zero FPS gain. I mean, the 7800X3D is literally the king for frame times cuz of that V-Cache. Better to save that cash for the NVIDIA GeForce RTX 5090 itself or a beefy Corsair RM1000e Fully Modular Low-Noise ATX Power Supply to handle the spikes. Be careful with those new chips, wait for benchmarks first! gl!

Seconding the recommendation above. I honestly think sticking with the AMD Ryzen 7 7800X3D Processor is the smartest move because chasing the bleeding edge is always such a massive headache.

I actually went through this with the last generation where I spent way too much on a flagship chip right at launch and it was super disappointing... had issues with thermal throttling and the performance gains were basically non-existent at 4K. With a card like the RTX 5090, you're mostly gonna be GPU bound anyway, so spending an extra $200-300 on a AMD Ryzen 9 9950X or the new Intel chips just to get maybe 2% more frames is literally flushing money down the toilet imo.

So basically, just save ur cash for the GPU itself since that's where the real path-tracing heavy lifting happens. I mean, the AMD Ryzen 7 7800X3D Processor is still the king of frame times because of that V-Cache, and it runs way cooler than the competition too. Lesson learned the hard way: more expensive doesn't always mean better gaming, especially when ur pushing 4K pixels lol. plus, you wont have to deal with the "early adopter tax" on a new platform. but yeah, good luck with the build! 👍

Ok so, before I give advice, what's ur total budget for the platform upgrade? r u trying to keep the motherboard and ram costs down or r u going full scorched earth with this build??

Honestly, I'm with the others on the 7800X3D being the current king, but if u are dropping 5090 money, u might want to look at the market shift coming up. We're basically seeing a weird transition where Intel is moving to a whole new architecture - tbh, it's a bit of a toss-up right now based on the rumors I've been tracking - * Intel Core Ultra 9 285K - This is the flagship for Arrow Lake. Intel is promising way better efficiency this time, which might help with those frame times in heavy path-traced games, but the platform cost is gonna be high.
* AMD Ryzen 9 9950X3D - If u can hold off a bit, this is the one that'll likely dominate. The Zen 5 architecture paired with the extra cache is basically designed for this exact high-end scenario. I mean, usually at 4K ur safe from bottlenecks, but the 5090 is such a beast it might actually push frame rates high enough that the CPU starts to sweat even at high res (at least that's my theory). If u can't wait, just grab the AMD Ryzen 7 7800X3D Processor and you'll be fine, but the market is definitely in a weird spot for builders right now.