Factory non-staggered 18's are +30mm for 8" width. Your new setup would push the wheels out +28mm compared to those. If you are running 17" 5-spoke wheels which are 7" width then the new setup will be +50mm further out. I never owned a G35 coupe so I can't say for certain.
My suggestion would be to go and measure how far outbound you have before the wheel hits the fender lip and then take that knowledge and run the information through a offset calculator similar to this one:
https://www.1010tires.com/Tools/Wheel-Offset-Calculator