plus different companies use different treadwear numbers.

 

FWIW I have a set of these on my (new to me) street E36 M3 and they are great. Very grippy and very quiet.

 

I have both XS and Star Specs in 205/50R15. No lap numbers and conditions were somewhat more favorable (cooler temps and mounted on an 8" wide wheel vs 7" for XS) for the Star Specs, but I felt that the Star Specs had considerably more grip than the XS on the track. They also seem to last much longer than XS. XS are almost down to wear bars after 3 track events, Star Specs are more than 60% remaining after 4 events and probably more street mileage.

I found the Star Specs very noisy (more than XS), and the ride harder on the street, with only a slight increase in steering response. XS have very nice ride quality, they even felt nicer than Falken 912's (both on 15x7 RPF1) on the street. They seem to round impacts off and make the car feel more fluid than Falken 912's, while delivering way more steering response.

I ran both tires at 27psi cold on street, and around 34 hot at the track. Does anyone have any recommended hot pressures?