What kind of abuse are you planning on dishing out?
The performance is probably a "tougher" layup, although I wouldn't take either one through a shallow, rock-infested river. I've owned a V10L Ultra and currently have a V12 Performance. Both seem to take normal handling without any problem; the lighter Ultra layup is definitely easier to carry & lift on/off a car. You probably won't notice a lot of difference between paddling the two layups, although the lighter boat will probably feel a bit "livelier" and more responsive, and the heavier layup will probably feel a bit more "planted" and stable. With the stable V10S I would lean towards the Ultra if it fits within your budget and you're not planning to run it through whitewater.