Shifting by 7500rpm, with that turbo, the cams are way too big - one would almost say the turbo is as well unless you spin to at least 8000, it qont stop making power there either on stock cams. You'll easily get 8200-8500 out of it (I did with my GT3040, span to 8500 stock cams).
You won't really make more than 300rwkw on 98. The GTX series needs more boost than 98 will safely support, which means E85 or you'll only just hover the 300rwkw mark on a good day (legitimately).
People have tried big cams with mid sized turbos, and pulled them out... So we know it doesn't work effectively