It comes down to ergos as others have suggested. For street riding I'd take the S4R any day. I just can't spend much time on a pure sport bike without serious discomfort. I also sounds like your track days will be occasional at most and the S4R is plenty capable on the track as well. Sure a very good rider will probably be faster on the 996, but for most of us the ultimate lap time is not the goal, but having fun and acheiving personal bests is. I do know a few, much younger riders that are comfortable enough on 996 and 998's to ride them all day long. If that's you then perhaps it's more of a toss up.