Both the 2600 and 3600 are way more than half decent; you can have some more single-thread performance by going with Intel but that’s going to cost a pretty penny.
The 3600X is 400 MHz faster than the 2600 and has IPC improvements owing to Zen 2, so you can probably expect some 20% uplift.
However, I wouldn’t recommend the 2600, but rather the 2600X: manual overclocking generally doesn’t net better results than XFR and is more work. Also, the 2600X is 2-300 MHz faster than the regular 2600.
Since the gap between the 3600X and the 2600X isn’t huge, and the latter was dirt cheap in the last round of sales, you might want to go with that, if your GPU budget could use the extra breathing room.
Personally I’d rather prioritize the GPU over the CPU; however, the game is still some 3 months away, so it would not make any sense to go very specific.