ive driven a car with a vortech, and it didnt make real power until up in the rpms, granted its not a procharger... but it is a centri. i have an intercooled 9psi kennebell on my ride, and i love it. it makes boost anywhere in the rpm range, i usually see about 7 psi around 1700 rpm and it climbs all the way to 10 psi at about 5900 rpm, its a pretty steady 9 psi between 2000 and 5700 rpm. my car has a stock bottom end, and i run 93 octane with a really safe tune. my a/f is 11.8 with 13 degrees of spark. honestly the vortech car had more rear wheel horsepower, but my car would eat that car alive at the drag strip, and i think mine is way more fun on the street. my car is making over 400 rwtq around 2200 rpm... i would like to see a procharger do that.
i have 4.10's in the car too, so for all you nay-sayers, im telling you its FUN, and as long as im relatively smart about it (not smashing the gas to the floor), it hooks pretty good, on 245 fuzion HRI's.