Thrash,
I suspect a Jett .25 or .30, or FORA .29 would be the absolute fastest motors out of the box, but price, complexity, and consistency dictate something a little less exotic for combat. In combat you want to run at the same speeds of others - not be too fast or too slow.

As Don "Tenman" Howard (so named for getting 10 cuts in one round at the world's largest combat contest) pointed out the Webra .25 GT is currently the 800 lbs gorilla in combat. But, it takes someone who knows engines, fuels and how to set them up to get the most out of them.

A mousse can from www.flyingzhobbies.com for $28 with a Macs header included will add 2,000 rpms to an OS, Norvel, or others. I ran Norvels in Open B but can tell you from experience they are not for the faint hearted. For more information on getting Norvels set up right go to www.georgiacombat.com, click on Technology link in Glow section and read up on them.

If it were me, and I wanted to have a lot of fun without excess expense or hassle, I would buy the OS .25 FX put a Flying Z mousse can on it and go reliably cut some streamers.