If you ask me a single mod which is the best for the gtr, I'd say it's the ETC. I don't know about other people, but this has been done to mine:
Profec B boost controller/OS Giken twin plate clutch/HKS air filters,Super drager,hiper damper,GT intercooler,oil cooler,turbo timer,iridium sparks,twin power ignition,ETC/Eibach springs/Nismo 3 piece magnesium wheels (only 9 lb each!).
Next things to do:
HKS forged pistons kit/264 cams kit/adjustable pulleys/either twin 2530 turbos or single HUGE TO4R turbo/fuel pump/air regulator/high flow oil pump/huge brake kit.
Result: 550-600 whp:flamer: :rocket: :aug2: :badass:
If possible: Carbon fibre body parts/6 speed sequential gear!
Hmm...that's about all for me. Anything more....I should save and buy the F60.