I knew I'd forget one. Yes, the Kumho XS is a good choice for autocross or a "dual purpose" street/track tire.

Regarding autox vs. track, I always recommend a lot of autocross experience before heading to the track. At an autocross, you can explore the limits of the car and beyond and learn how to recover. (as well as what you can't recover from) These are not things you want to attempt to learn on a race track! But, they are skills and experience that will save your butt when you make a mistake on the track... or more likely will keep you from making the mistake in the first place.