Awe man!! That is AWESOME!
You are going to love that card. If you are going to be mostly gaming, I suggest 32-bit Mint, but if you have more than 4 Gigs of Memory then you would be wasting it.
I have no proof that games run better or worse on 64-bit, so as long as you install the "multiarch" 32-bit libraries, you should be on your way.
Just make sure to install 32-bit Wine, 32-bit PlayOnLinux and all your games in a 32-bit virtual drive.
I think PlayOnLinux scripts still ask if you want a 32-bit virtual drive?
But I know for sure manual installation does.