Probably the best possible CPU is i7-2600, as while chipset Q67 supports 2600k, i don't see official support of this motherboard for it. Anyway, even if it can work, 2600k wouldn't make difference in this particular motherboard.
Should be compatible as long as the socket is the same. So, I'm not sure about old motherboards, but an entry level motherboard from AMD (a-series motherboards) would have trouble handling a Ryzen 7 (Equivalent to an i7) So you may want to see if the chip set can handle an i7. My guess would be yes.
Probably the best possible CPU is i7-2600, as while chipset Q67 supports 2600k, i don't see official support of this motherboard for it. Anyway, even if it can work, 2600k wouldn't make difference in this particular motherboard.