actually ur 6th gen got stopped by wind resistance. when i put on my 16" auto-x rims i hit 140mph before hitting the speed limiter. On my 18's i can max out 4th gear (which calculated speed is about 135mph) but 5th gear doesn't have the pull to get to 140mph per speedo which would be almost 150mph.

Anyways the governer will only kick in in 5th gear when ur speedo reaches 140mph. Unfortunatly unless ur going downhill with tail wind it probably won't ever happen on stock tire size. My 16's did it because the actuall speed was slower and the gears had much more pull.