The 458 Italia with Lexan, CF hood, 30lbs downforce will put you around 625bhp with all other obvious add-ons. Don't lighten the car. It outhandles a stock Enzo and is much quicker through any exchange. Trail-brake like a mad-man and set your suspension hard. Even though you're restricted to sports soft, trust me you will out-handle the Enzos even on GP/D and Toscana. The motor is so balanced that you should only downshift to 3rd in most corners and set a higher top-speed on your tranny. So obviously with the pooter tires, the LSD requires a fair amount of throttle feathering in certain sections (I.E. off-camber elevation changes through chicanes, etc).
The Enzos suck to drive with; they plow and have an awful weight-transfer transition under loss of downforce and rear traction. Theyre only true strength is straight-away speed as theyre commemorative, purpose-built racecars. They have too much power in the last 2 races for a max-built & lightened F430 Scuderia or 458 Italia. Trust me, I learned the hard way after breezing through the first 3. GP/D was where I couldn't even catch the 2nd-place Enzo with a maxxed 458 or Scuddy. See above and enjoy the winnings and the most expensive award car in the game which is also conveniently your rewards max.