The above offsets u quoted are more suited to RWD GTSTs. You have a GTR, take advantage of this!! Due to wider guards, GTRs can run offsets between +15 to +20 depending on wheel width. Something that us, non GTR owners envy.
Smaller offset wheels also normally translate to more dish and aggresively angled spokes which make them look much hotter than if the same wheel was on a GTST...if that makes sense..
Oh and yeah...for a GTR, try and run 4 of the same width n offset wheels all round.