The GT25r and GT675RS are two very different turbos. I remember seeing posts that a few people had alot of trouble making over 400rwhp, which kind of makes the GT25r more or less a ball bearing version of the stock turbo, but not really. Just has about the same power output from what i read. Go with the GT600r kit from Z1. Thats supposed to be entirely bolt on. Not sure if it comes with the downpipes though. If you go with the 675RS your going to want to do some head porting and get some manifolds to make up for the lag as well. 600R is standable with out manifolds, but a member here stated that with 530's + Dupree manifolds there was almost no lag.
