Yeah, I'm looking for everyday street power, so I'll pass on the funny gas.
I've read that the procharger systems are heavily upgradeable. Is the Whipple? Can the procharger be upgraded to provide more power than the Whipple?
Yes. Prochargers and all centris in general are very upgradeable and can be scaled to whatever power level you want. The D1SC will do fine for your needs, that's the standard head unit. You can easily swap head units at a later date if you decide to go built motor/Trans and big boost. There's also tons of options for intercoolers to get your IAT down, since with a centri you can put any size air to water or air to air cooler that you want, because you just plumb it in before the boost pipe gets to the throttle body.
With a Whipple, you're limited to what the stock heat exchanger can do, since it's under the Blower, and the unit replaces the intake manifold . but, the ram kit uses the bigger 2.9L unit which supposedly has a larger heat exchanger, and is capable of more boost. It can still be upgraded with pulleys to make more power than your stock block or Trans could handle.
Kit for kit, the Whipple will make more low end torque, and all around performance, and be capable of more power than the D1SC procharger that comes with the kit. But you can also buy procharger units that support over 2000hp, so as far as which is more upgradeable, procharger takes it.
Can someone ask "Them" if that's 600hp at the wheels? Lol
No. People are running 500-525 whp in much lighter challengers and chargers, single cab trucks, etc.
I don't know personally of anyone who has pushed a stock 8HP70 to 600whp reliably on a truck, but my experience with transmissions tells me that 600whp on a 5800lb truck with 37" tires is not going to do any favors for the transmission.
600whp is also around 750 at the crank, and that's pretty far beyond what the stock internals of the 5.7 will handle. So you'd be in built motor territory at that point.