If your doing trackdays then I think the S4 has less ground clearance unless you change to high level cans and rear sets. Though I have heard the S4r is easy to deck out on track to if you go for it
on the road both be fine i expect.
The S4 is 916cc and S4r 99c so more power. Best reason for the S4r for me is the single sided swingarm looks so cool
[Edited on 31-10-2005 by Lee1980]