True stock engines seemed to only hit about 5800RPM. In the beginning it was the same mess, rules said 10.8 springs so the race was on for the rule bending 10.8 springs which would go soft on us after a few events. Another track across the border was running ASN Honda GX200's with 18# springs and they were stomping us with the ability to run ~500 rpm faster and they were also not chewing up the valve train. As we got more racers and I'm a big guy I went modified anyway, but a lot of the others slipped in the Honda springs to put an end to the spring game. Around our 19 turn sprint track, the Lo206 has just turned out to be much faster than the clones and no one is running them anymore. Our last guy to change over, was two seconds a lap faster pretty much instantly when he mounted his new Lo206 package, I think they just have more usable torque and come out of the turns better. Dyno tests done locally show the Lo206 with a broader torque curve, and the clone with more top end power.
Being you are running a smaller oval, the clone may have an advantage depending on how much speed can be carried in the turns.
What we did at our track was simply set up a catch-all, and adjust with weight (kart and driver). We've got L0206 light @365#'s , World Formula light @420#'s, and the occasional clone engine which has been dropped to 335# for stock. Heavy class is 390# for Lo206 and 435#s for the WF(what I run). Our last race of the season last year, the top 13 karts were separated by less than half a second on a 1-minute per lap track.