i would recommend checking out google... i don't have the 7400 but i do have the 7200 and mine is running @ 4Ghz 9.5 X 422 ( that's 58% overclock ) and it's 80 F in here and idles around 43C I am using a freezer 7 pro with arctic silver thermal paste
that CPU has a 11.5x multi, which high multi is awesome(IMO) for overclocking. though you should push up your vcore abit, and you should be able to hit 4.0Ghz farely easily. the E7600 can hit 4.7 on air i've herd, so yours should be able to hit 4.0 24/7 easily.