seeing as u are still on the stock ECU.... i'd say not a lot, your also missing a boost controller...

*Greddy Profec B
*Simple Digital Systems EM4-F or Microtech, or E11

now your set for 500 wheel HP.. weather or not u make it is determined on ur mechanic skill and about a years time... your pocketbook will take a healthy beating....

dealing with your turbo (now that i just realized it) Ever thought of going Ballistic Series?? Enthalpy improved almost 70 wheel HP after a switch to a GT30 and some more tuning...