Um i suggest you stick the with RWD NA R34 they are lighter and faster then the 4wd version, ill only ever get a 4wd skyline if its a GTR. Anyway the years well it does not matter what year R34 skyline you get, i got a 1999 and my mate has a 2000 model, the oldest model is 1998, and i think they only go up to 2001, but i have never seen a 2001 for sale i probaly did but forgot i have seen it because its rare. Now there are two types of r34 Skyline series 1 and series 2, and they are distinguished by the front bumper, seats ( i sometime hacve problems telling this apart), Wheel ( the series 2 has the GTR looking wheels), series 2 has bigger brakes ( my mates tells me its got GTR brakes but im not so sure), the steering wheel is diffrent, the gauges ETC but there only cosmetic differnces that have been changes a little, to be honest i like the series 2 more then series 1, but its harder to find a series 2 so i just went for a series 1 instead, i didnt really give a crap because when i saw my series 1 i had to have it lol. So if you want some cooler cosmetic differences you could get a series 2. Otherwise there is absolutely no differnce in performance, reliability ETC bettween the 1998-2001 r34 skylines, it all comes down to how they were treated by there owners E.G a 1998 r34 could be in better condition then a 2001 which wasnt treated with car, services ETC.