^^^I used to get beat by a Diesel Rabbit! Let's see, also got my butt handed to me by stock;
Buick Regal Ultra
'94 Neon R/T (very ratty, with a driver on the way to Nationals)
Grand Prix GT
and probably more than a few other in my first season!
Stock I have beaten
Factory 5 Shelby Cobra (3 so far
All much faster cars, with noob drivers. That diesel Rabbit had shocks and slicks, but probably wasn't kicking out the 68bhp it came from the factory with. The guy just kept it nailed the whole time and carried every scrap of momentum possible through the whole course.
Unless you are just dying to mod, I would say even hold off for a while and get to grips with what you feel you need the most when you are on track, and of course just get as much practice as you can.