I've used two sets now 225/50/16 and a 255/45/17 on two different cars (Z32 and a R33 4 Door).
Great tyre that loves heat cycling; great for short-medium work RE55S's IMO are better for track work; The R888's come up to temp very quick but tend to overheat a little bit with continuous hard track work - least in my experience.
Great wear on them, and even when nearly a slick still perform extremely well.
I originally chose to try the R888's becuase they are a directional rather than an asymetric tyre (the RE55S). Barbagallo Raceway in WA tends to wear the front left alot harder than the others.