I think the factory GT500 motor could probably win this debate, even eclipsing the Supra 2JZ. With a blower swap and pump gas friendly boost, I have personally seen over 700rwhp. If you put the coals to it, I'm sure over 1000rwhp would be attainable with a factory stock long block.

YouTube - Evolution Performance, Inc - Shelby GT500 Runs 9.34@147mph

Here is a link to some guys going low 9's with a stock motor. This is a little dated, and people may have gone faster by now.

Brian
EFI-Unlimited