I have 3.73's and I was in 5th gear. I am not exactly sure how much power I am making, but I trapped 123 mph last time out with a stinky slipping clutch. At a 3000 lb race weight it should take about 400-420 rwhp to turn that mph. I guess that comes to approximately 500 crank horsepower, or 180 hp at the wheels on a Mustang Dyno.
(funny if you read the thread....)
It also did not seem to take too long to get up there either. Hard to judge though when you are all adrenalized in the middle of it.