I don't think have that car but if you did this to the car:
1. an oil change before running it
2. Racing Exhaust
3. Racing Chip
4. Engine Balancing
5. Port Polish
6. Turbo Kit Stage 4 or 5*
7. N/A stage 3*
8. Supercharger *
NOs and the 3 weight reductions phases also help you get the most out of your car
If you've done all of the above, that's as good as is gonna get. This is regarding Power in HP of course, but all of the other upgrades like suspension, transmition etc...help you race better, and most of the time, if you know how to tune it properly, the HP goes unnoticed.
* Whichever is faster and applicable.
BTW don't expect too much from nice cars like those...same impression I had from my 350Z GT edition, I could only manage to get 489 HP out of it
Ciao...