600 on fuel is just too tough a pill to swallow for most people ($$$ wise I mean). It just takes too much. I think upper 400's to 500'ish is a pretty realistic goal with 190's and a good single turbo upgrade. I think that's about at the limits of streetability with these trucks. Unless you have the coin for twins and other custom parts/labor... I surely don't. Getting to 400HP is relatively cheap. That extra 100 is going to cost you about $8-10k if you figure in a tranny.
Of course I'm referring to getting HP on fuel only. You can always spray your way to 500... for less $$$.