There is a review online somewhere, where it compares the R31 and the VL commodore. I believe they said that that the aussie skyline had a better build quality and had slightly better handling than the equivelent VL. Knowing Nissan compared to Holden I'd say that'd be true.
Well my old R31 was up to about 280,000km before i sold it still going strong. They have a very strong engine (capable of some 350,000km) if treated well.
The power output on the R31 is 8kw up on the VL for some reason (different exhaust?)
try www.r31skylineclub.com -- they have some old articles on there.