Whoopsy:

So they souped the GTR to around 700hp then. 

Whatever it takes . It's called  " run what ya brung " . 

Nothing new here  and each of these official times posted by a manufacturer surely includes " optimizing " every parameter of alignment ,engine ECU, traction mgmt ,etc -but staying ( you hope ) barely within production tolerance ranges -  for that course vs what is normalized assembly line production of  what they give you, Joe Customer ,  off the delivery truck at your dealership.

So since they all do it, the comparo times still have merit.