The only real difference is an extra groove around the edge of the tyre / wall but, as said, the S is no longer in production.
I always found the T1-R's to be fantastic in the dry and fine in the wet. I never pushed the car in the wet and they never surprised me or did anything out of character. Other tyres may have better wet handling, but if you're pushing your car like that in wet conditions, then you're asking for it IMO....
A good cheap tyre, although other brands such as Goodyear F1's, Contisports and Pilot Exalto's are better overall quality and seem to last longer.