Games are more demanding on the GPU than the CPU, but a 7700K is still quite capable and should not slow you down in general OS usage. This sounds more like a storage issue - games tend to load everything before you start playing, whereas browsers and other applications are constantly reading/writing to the cache, etc. I'm not convinced it has anything to do with free space remaining, and I'd be more suspicious if something is keeping disc usage at "50%" - in fact, I'm pretty sure Windows calculates it in such a way that 100% usage on one drive would show as 50% in a system with two drives. (Additionally, if one drive is completely full and your games are on the other