I'm running 553bhp and 465lb/ft torque. I have the RaceLogic Traction Controller http://www.racelogic.co.uk/index.php/en/racelogic-products/other-products/racelogic-traction-control (by the way, as of yesterday we are an official appointed RaceLogic reseller, so expect a FAIR price). I've changed the tyres to 305 rear and 265 front. At the moment the car is an animal and a half, but controllable. To improve it further, I'm changing the diff with a Quaife diff: http://shop.quaife.co.uk/nissan-350z-auto-quaife-atb-helical-lsd-differential
Where do you leave? If you're not very far, come and I'll take you for a demo drive so you can see how the car handles, that will give you some ideas about what can be achieved.
Also speak to dajw in here, he runs a 370z Stillen SuperCharged 370z, very stealth, standard suspension, wheels, diff etc.