I’m looking forward to trying the RT660 after reading GRM’s review. The RT615K+ is an excellent long wearing 200TW tire for the FiST, if you’re stuck with 215/40/17 tire size. If the RT660 is an improvement, I’m game to try it. The Yoko A052 looks good too but it’s a bit more expensive than the RT615K+ and RT660. For the price of the A052, I’d probably run the Nanking AS1 r-comp.
As for the Indy’s, I use them on the street. They don’t have anywhere near the grip a 200TW tire like the RT615K+ and 595 RSR or RS Pro have, but they last a lot longer and they’re cheap. The 595 RSR is a decent street summer tire. I’ll probably run them again when the Indys are shot. I don’t recall the RSR being loud and they were fine in the rain when I had them. They’re just not track worthy and that’s what I bought them for.. I’m also not a fan of the RS Pro on track but that’s another story.. The older RT615K was great. The RT615K+ was a noticeable improvement. I bet the RT660 is awesome.