You can put GTR wheels on a Z, but you'd need to downsize the tire profile in order to get the overall wheel/tire combo to fit. Ben have you looked at 19" winter tire setups? plenty of people run 19's on the GTR....
Ben, don't price out 20" winter tire setups they are ridiculous... look for 18's or 19's. and take it from a guy who has gotten TPMS put in all of his aftermarket wheels.... just dont bother. i never even got mine synced. deal with the light for 3 months of the year and put your summers back on.
wheel sizes and tyre diameters that near match OE
20" wheels(standard)
255 40 20 = 712mm
285 35 20 = 707.5mm
19" wheels
255 45 19 = 712mm
285 40 19 = 710mm
18" wheels
255 50 18 = 712.2mm
285 45 18 = 713.7mm
18" wheels that fit (make a sticky pls) - GT-R Register - Official Nissan Skyline and GTR Owners Club forum
look for some cheaper 18's you can easily get a winter tire/wheel setup for <2k maybe even <1500.
I'm down to go to the drag strip in spring. I dont really have time right now and its cold :P march i'm down to go.