Both coolers I suggested support 120mm fans, so yes you can swap/add more if you want.
the CFM of the cooler isn't... super important because it's more important to get air into the case, where higher CFM matters more.
And higher CFM = higher noise, so the more expensive one, with lower CFM still cools better.
The gammax is like, 1-2C worse than the 212, but if you replace the fan(s) it may run better, and it's also short enough to fit where the 212 wasn't.