can probably go higher then 4.5ghz---4.7ghz area as long as temps are ok and not using too much voltage
my 6600k is at 4.7ghz and will probably go more as got full watercooling but too much time is needed to overclock and test it out once you get near the limits
of what it can go to so i just shoved it straight to 4.7ghz and left it there--one day will get round to seeing how high it can go