hey stryder, for what its worth imo for 250kws going all out on gt-rs would be delightful, if you have deep pockets
i however don't so a cheaper but still far capable option would be T517z's with 8cm rear housing to suit your quick spooling lust. also available in the 10cm rear too which is not a "laggy" turbo by any means.
if you were going to go nismo 555 you may find the price between them and sard 720 perilously close..just another something for you to consider i guess.
what is your car doing at the moment fuel pump wise.?
best of luck anyway dude