Not a whole lot. LS2 six speed manuals pull about 335whp, and his was rated at 393. GTO's are just fast fucking cars, period. The bottom end is plenty strong enough to run a 150 wet shot with no issues. 485whp would be about an 11.0 car with a quick shifting chica at the wheel.
Many peeps are gotten awesome service out of the autos. It seems to be kinda hit or miss. That's why I want the manual.