Not sure if anyone in this thread has a PH Turbo so I'll chime in. The basic kit with nothing else will eaisly make 500RWHP and over 500WTQ. I've got mine with a conservative tune and I'm making 480RWHP 16 timing and AFR is under 12. So if I wanted to crank up the timing a little I could easily make 500RWHP. The kit when I purchased it was around $5500 count on another $800-1500 to install it. The only other thing you might need is a MAF Extender as I was close to pegging my MAF with the 11# spring. Also you better consider upgrading your clutch at the same time. The stock clutch is only rated at 380wtq I'm making 515wtq and my stock clutch is starting to slip a little only after about 2-3k miles with the kit.
I've attached a pic of my dyno. Custom tune is required so plan on spending another $350 on the tune.
Turbo or S/C really depends on what you're going to do with it. Here's what I learned on my 5.0 SN95. I had a Vortec S-trim centrifical s/c for 2 years, then changed to a twin-turbo with intercooler.
As I understand it, there are basically 2 types of superchargers, the centrificals and the screws or roots. The centrificals mount like an accessory (alternator, a/c compressor, etc.) and produce their boost pressure more at higher rpm's - which makes them great for drag racing at a strip. My Votec produced 10# of boost at 6,000 rpm's.
The screw/roots types mount in place of the intake/plenum and make most of their boost pressure at lower rpm's - which makes them great for street driving. Most factory s/c cars use this type for that reason. In either case, s/c's are always being turned by the engine/crankshaft and pulleys, and always pull some power off the engine - more as you build boost pressure.
Turbos rely on exhaust pressure to build boost pressure. When you keep your foot out of it, they're just going along for the ride and drain no power from the engine. As you put the engine under a load, exhaust pressure builds and causes the turbos to spool up - building boost pressure. The time it takes for the turbos to spool up is referred to as turbo-lag and it can be significant. Generally speaking, the bigger the turbo, the longer the lag - that's why you see twin turbos. Using twin turbos you can use two smaller turbos, but get more boost (like a bigger turbo) and reduce the lag time. My twins gave me 10# of boost at 3,000 rpm's, which made my stang much faster and more fun on the street. I did have problems blowing headgaskets even with the ARP head-studs and good Felpro gaskets.
In hindsight (which is 20/20) - if I had gone with a screw or roots-type s/c, I might never had changed to the twin turbos as I would have had the better low end torque for street driving. Also, I had selected the larger twin turbos for my kit, which in hindsight I didn't need to do. Had I gone with the smaller ones, I would have had less boost, but got it sooner. I think 6-7# of boost would have been plenty and probably not have had the headgasket problem.
I've heard that 7# of boost effectively doubles the amount of air going through your engine and most factory setups don't go past 6-7# (exception was the 86 Regal GN I had which had 14# from the factory). Keep in mind that more boost means more fuel and the need for bigger injectors &/or more pressure, bigger fuel pump...
So that's what I know about forced induction. I think I'm correct at least on most of it, but I'm sure that if I am in error - there will plenty of members to point it out.