I lot of it depends on luck of a good chip, good VRM's from a decent motherboard, and keeping the socket cool. The socket usually hits the thermal wall long before the cores do. In order to get my 4.62ghz stable on my 8320, I have a small CPU fan hot glued to the back of my motherboard to get air on the back on the socket and keep it cooler.
That motherboard has 4+1 phase VRM so not the highest. You could probably hit 4-4.2 or so with it. My old Asus board was similar and that was about the max I could hit before upgrading my motherboard and adding a socket fan to it.
Really it comes down to what your chip will do and what your MB can take and that varies for every single chip and MB out there. 2 exact setups can hit different max's.