What render settings have you tried?
How complicated is your comp? (tons of particles with trapcode particular maybe?, motion blur??? those are definite resource hogs)
Are you utilizing all your available processor cores within preferences / memory & multi-processing?
Although I think you might have a setting problem, you shouldn't be having any problems whatsoever with an i7 OC'd to 4.2GHz, go into your preferences and see what settings you have set.
Have you tried H.264 at say 1080x720, 24fps? Those are the settings I use for HD YouTube without any problems...
Maybe you don't have enough or are running out of ram, I always hover my mouse in the timeline or the viewport and do a crl+alt+/
(/ on the keyboard) to release all the ram that was previously stored into memory while working.
