One thing you might also want to consider is the class or PAX rating your car will get at an autocross with "R" compound tires. Going with the 615's or any other tire that has a wear rating greater than 200 means you can run the stock classes or at least get a lower PAX rating.

Of course for DE's it's irrelevant.

I just got the 615's on my track wheels today, here's my first impressions.

The tires are not terribly loud and seem to have a very strong sidewall. The steering input is very precise with little tread squirm and a low slip angle. They are new and I haven't heat cycled them other than the one run home but their traction seems to be very good with a very linear breakaway. I won't know for sure how well they work until the next auto cross but so far I like :D

Oh, and the tread pattern really looks good on the car.......