585 hp from slp is able to do 0-60 in 3.6 and 1/4 in 11.5@122 by motorweek's testers with pilot ps2 tires and short throw shifter......so maybe 585 might be pretty close to what GM will offer in the Z/28. This is some of the best times that I have seen with a tuner camaro by any online magazine or tester yet.
Video posted @ this thread:
http://www.camaro5.com/forums/showthread.php?t=123899