Anything much over 600cc's in a two stroke will slow it down, due to the mass of the piston. The ATK 700cc would only rev to like 3500rpms and would put it all to the ground. I remember reading an article about it saying it was pretty much a flop, due to the overall weight.
If you are going to go to those sizes, you seriously need to consider an inline twin. But then you have to deal with the mass and weight of the engine. Both ways, a 500 is VERY capable of running the same 1/8th mile as an inline four 1000cc bike with minor mods.
The biggest improvement you can do, powerwise, is correct the jetting. Then comes the huge list of extras that give minor, but add up. So, with that said, if you are not getting a small amount of surging, your jetting is off. Call me crazy, but I get all kinds of surging and I can run a faster 1/8 (1/4th mile gearing permitted) lap than my street bike ('05 R1). That's performance.
I do local drags for fun in Smithfield, NC at an ATV park with a 1/4mile dirt drag strip. Mainly drag Alky and in-line four (600-1000) quads. But every now and then will get a KX500 or CR500. Most sit back and watch though. For racing, I head up to Burkeville, Virgina and race a 1/8th mile grass strip.
