[blykins]

Allow me to hop on a soap box for a second. Lots of guys want 600-700 hp but they are not willing to put up with it or buy the parts to support it. If you want something that is over capable of handling the power without chatter, you need a twin disc. If you want a single disc, you will most likely run into some chatter with the ceramic and sintered iron discs because of your rearend ratio. If you want a single disc clutch and no chatter, you don't really have a choice. A 500 series disc will most likely work just fine. But the instant you bolt on a real sticky tire and start driving aggressively, you will approach the limits.

A 600 series disc isn't cheap. At your level, I'd pay the $700 for a twin disc.