Guys are running 8-10 lbs of boost with an intercooler and methanol injection pulling 650 HP with most engines from the 5.3 to the 6.0. Put you some forged pistons in there and drop the compression and then you can run even more boost for more power. I'd suggest larger injectors closer to the 60 range for performance. There are a lot of guys running the STS kits on here and I don't know of anyone unhappy with the results.