I have a j35a4 with a t3/t4 turbo with a 5.4lb spring in the wastegate. Running on pump gas. I hear that you can run up to 9lbs but that is about it with out rods and pistons.
Depends how big you wanna go. haha If you wanna go real big, you've gotta time your trip when guys like Parsons and Renner are out there then scope out their lines. I'm hoping they do another one soon. Parsons seems to be out there quite a bit these days.