Back on topic:
I think a turbo upgrade is priority #1 here. My first recommendation would be for the ksb1-b lightning. Spools like an HX35, but supports 430 hp. It's tough as nails too.
If you're not into the B1s (and their $$), then the hybrids seem like a great options. The HTT with the 63mm wheel is an awesome turbo, and I think that the Dodgezilla is now available with a 63mm wheel as well.
The thing to keep an eye on in the altitude is turbine housing size. It HAS to me carefully matched-- to small and you choke flow, resulting in high EGT. Too big, and you lose too much boost, resulting in high EGT.
I would favor the B1, because you can get a great turbo that spools in a blink and will handle 430hp easy (just #2, much more with drugs or water/meth). If you want, you can swap the housing to the standard size (keeping the small turbine wheel) and be good for 475HP easy with less spoolup.
Justin