Hey Steve,
Hope to see you back out here...
Based upon this years National results, all STS cars were shod with either BFGoodrich GForce Rival's or Bridgestone RE71R's.
195/50/15 was the "chosen size" for many years due to lower unsprung weight, plus the cheater compound on the Toyo's....but more and more are moving to 205/50/15's. (Rival's aren't avail in the smaller size, which plays into that too.)
I'm personally still running the RE71's, as are Pete & Gary (our other local STS Miata drivers)... but who knows what next year will bring. I haven't really though about it yet.