Friend/Customer of ours we did the swap for in the white 240z i posted a video of him launching a while back is running 256whp and 252wtq on 15psi and these are his mods: Greddy intake manifold, full 3" exhaust, custom fmic, tial bov, blitz boost controller and walbro gsl392 fuel pump with surge tank as well. Yes the stock turbo is a T25, you can run 10 psi daily and 15psi every once in a while, but 15psi daily on the stock T25 would kill it really quickly.
Here is the link to the video i posted a while ago:
http://www.vildinimotorsport.com/gallery/images/mattlaunch.mpg