I've heard of guys with the STS dynoing about 570 rwhp, I just can't remember the details. I would have to look them up. I think it was unertaker who had about that much hp... before he went with the forged motor. Btw, haven't seen him here in a while. Look up his stuff... you should be able to find some good info on there.
p.s. - I'm with you on the turbo decision... I like the idea of having boost on command with a boost controller.