Looks like the 5000 is an easy overclocker gets to 3.2 fairly easy from what I've been seeing. Don't know to much about the 5600 though.
3.4 Gs on air is one of the better marks I've seen. I take my 5400 to 3.355 and it sarts to struggle. Extra volts does seem to make much differance, haven't tried to go over 1.40. That and I'm pretty much just using AOD.(To lazy to pull off the side case and reset the bios.lol)