Hello @Camaro_SS and thanks for posting on the Microcenter Community Forum. To answer your questions, if you want to attempt to get the max performance out of your CPU, than go with the 5950x. With your build, the 5950x is within your budget. Is it necessary for your currently part build to upgrade to the 5950x? No, your build is fine with the 5900x and its 12 cores. The 5950x is a beast, but for what you're trying to do based what you described how you'll use the PC, the upgrade really isn't necessary.
The RX 6800 XT vs 6900 XT, there's not a huge performance difference between the two. Of course 6900 XT is a slightly better card, but its overkill for what you've described how you'll use your computer. The 6900 is within your $5K budget; if want a slightly better performing card, then upgrade to the 6900, otherwise stick with the 6800.
Overall your build looks good. You matched up a good motherboard for your Ryzen CPU, PSU, RAM, etc., all looks good. The only item missing is your Operating System (OS). You'll want to add a Windows OS cost into your custom build total. But everything else looks good.
The 5950X is a very specialty part and does not help with gaming compared to the 5900X. 5950X is more for pro video editing and similar. Google for "5950X vs 5900X gaming"
I have a 6800 XT and I assure you it will rock your face. The 6900 XT costs almost 50% more but is only something like 10% faster. Honestly, it isn't worth it and you won't even notice the difference.
On your list, the H100 is a medium size Corsair cooler. Consider the H115 because a 280mm radiator is a LOT more capacity than 240mm. 39,200 square mm versus 28,800 sq mm. That case's spec says a 280 fits. Both 5900X and 5950X generate a lot of heat.
AMD makes all the Radeon GPU processors and sells them to misc graphics card makers, called "AIB"s (which stands for Add In Board). Basically the difference between video cards all comes down to the coolers and the customer support. I bought a 6800 XT straight from AMD Direct (Google for "AMD Direct US") which is the ones AMD themselves put their own GPU cards and sell them. The cooler they slap on their own cards is rather cheap, which is what I wanted since I removed it and used a water block instead for liquid cooling. If you are not going this route, then get one of the AIB branded cards.
So really it comes down to who makes a better (more expensive) cooler. One with small fans and less heat pipes on the exact same 6800 is slower than one with more, larger fans. Because internally all the 6800 will self regulate its own speed based on how hot it is running.
MicroCenter frequently stocks a brand called PowerColor which is a decent brand and they specialize in AMD Radeon. Supposedly they carry a few other brands like Asus and MSI but with the current market those inventory almost never show up. Really the only thing you want to check is that sometimes the triple fan cards can be really long, so look at the case specs and it will say something like 'max graphics card size is ...' and then make sure the model card you select will fit (and don't forget to leave space for the CPU radiator cooler). If you're going to buy it all at MC, I recommend you go with the PowerColor 6800 XT Red Devil Overclock triple fan. Oh, and if you didn't notice, there is "6800" and "6800 XT". The XT is the absolute best price to high performance ratio.
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