+5 to checks for those stats. For both classes that is a Primary Requisite. I think it is also the stat that they use to generate to hit chance (part of it anyway)
But how significant is the difference between +4 to +5?
+1 to your Dex for example can be the difference between you hitting the enemy and he missing you. Its all about small increments.
But feats on the other hand can drastically change how you play a class.