The biggest problem I see with this is you need 2 wastegates and you need to run more piping, meaning more money to spend.

To OP, Garrett came out with a new turbo dubbed the GTX series.
Here's the 3076R.
http://www.atpturbo.com/mm5/merchant...egory_Code=GTX
I'm planning on going T3 too but I'm getting the 3576R. From what it's advertised as, it spools as fast as a 30R but makes power like a 35R. It's a turbo that will for sure get you your 500.
http://www.atpturbo.com/mm5/merchant...egory_Code=GTX

Otherwise, you can go with the tried and true HTA76. Spools faster than the turbos above and that price comes with a hotside. Those GTX's don't come with a hotside and you have to buy it separately.
http://store.forcedperformance.net/m..._Code=Turbo-FP

 

you should chose smth like 6262 definately not FpBlack, I jsut changed one for 6262

max for Black on pump is around 450whp

 

How much power are you seeing with the 62 and how much psi?

 

I have seen the EF4 make 500whp on pump/93 so I do not see why any 30r cannot achieve the same.

 

I didnt do dyno yet its to cold in Ukraine ATM, but at OFF I have 1.2 bar and my double pumper with single line is finished, I did install second fuel line and that shows that definatly more than 400whp, because on Black at 1.2bar I had 400 whp