I also have the Firestone Indy 500 and would agree with what you say about their grip. They do give up a little bit of the quick immediate turn in that the OEM Bridgestone Potenza RE050A tires have, so I considered two going back to those, but they were unavailable on Tire Rack last time I looked. The local Firestone dealer quoted me a really high price of about $1350 for a set of four mounted and balanced, and they also had to special-order them, which I didn't like because I like tires that are readily available if I damage one and it can't be fixed.
For the combination of decent performance, good price, and ready availability, I think the Firestone Indy 500 are currently the best bet. This is assuming that you don't want to go with an Extreme Performance tire, which I didn't because I run them all year round, it doesn't snow enough to justify winter tires here in North Carolina, and figured they would just be really really bad in cold weather.