to answer your question, i'll pass it to temujin or pimpin or v-spec to answer it.
all the skylinExpert
Among the diff. ways to tell (from other forums):
V-Spec over Standard GT-R has
* front splitter and diffuser
* rear carbon diffuser
* lower stiffer suspension
* exhaust temp and intake temp sensors shown on MFD
* ATTESA E-TS Pro + active LSD at rear
V-Spec II over V-Spec has
* aluminium pedals
* brake upgrade on rear
* carbon bonnet with naca duct
* slightly darker iridium console
* black door trim and seats with white stitching
* more stiff suspension
* clear front indicators