Depending on what level you were racing shifter karts at, I'd suggest that nothing within the SCCA Club will. Good luck to you and let me know if you find it.
In my opinion, very few people who have both the money and the skill to race wickedly fast cars find themselves racing for a hobby year after year. They usually have one or the other or they wouldn't be here (for the most part).
I haven't driven anything as fast as DaveW, but I have driven some cars that were much faster than others. In my experience, the fast thrill/mind-body overload you get in the beginning wears off pretty quickly and it doesn't feel excitingly fast for very long....usually at about the same time you are chasing somebody and the ride is no longer fast enough....until **** hits the fan. Then you suddenly are reminded just how fast you were really going.
Concentrate on finding the competition. Or if you want to go fast build a FS car and forget about the competition, just keep building it faster and faster until you run out of money or talent.