Not quite an apples to apples comparison. The 4S is a 300 treadware street tire, whereas the RT660 is a 200 treadware mixed use street/track tire.
On track, the RT660 would be orders of magnitude better than the 4S. On street, it would probably be hard to really tell the difference, but the 4S would likely last longer.
I run RT660 on my gen 5 Z/28 and find that they provide comparable grip to many r compound tires in the 100 treadware range that I've run, including R888R, PS Cup 2 (180 tw), NT01, and F13R.
I've run 4S on an M3 at the track once and found that they were extremely noisy at the limit and performance fell off dramatically as the tires warmed up.
If you're tracking the car, the RT660 all day. If you just want a nice performance street tire that will last long, then go with the 4S.
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