From what I've seen so far, no matter the cooler or the board, Ryzen 7's stock speeds are already about as fast as they get. OC potential with these chips is very low. Many are only getting about 100MHz OC out of them.
Ryzen 5 will likely have more room for an overclock.
As for gaming, Ryzen 7 is not your best choice. Ryzen 5 will be better for gaming. You'll lose a few cores (the games won't really care), and you'll hopefully gain some OC potential (the games will care about this).