The Greddy TT kit has already landed in the UK, will be delivered on Monday, can't waaaaait!
Meanwhile, looking over the US forums, some crazy numbers achieved on stock internals:
2012 370z Nismo 6MT Greddy TT at 15PSI - 637HP & 506TQ
2011 370z Nismo 6MT Greddy TT at 9.5PSI - 560HP
2010 370z 7AT Greddy TT at 7.5PSI - 480HP
2009 370z 6MT Greddy TT at 8PSI - 524HP
According to Greddy, the kit is able to reach 850hp, with proper mods and forged internals.