I ran my GT10 10.5/4cell against some 19T/10.5 touring cars last night and the speeds were quite similar. The TCs came off the corners better and had more braking abilities, but the GT10 had more corner speed and the same top speed in the straightaways.
I still don't have the correct tires, and my Viper body lacks enough downforce for the speeds we're reaching (140ftx70ft), so the TCs were still beating me (although I'd expect it from L.Fairtrace and his psychotic Losi 13.5). More testing......