I've owned both and in stock form the Suzuki will be faster in a straight drag race. When I had my 400EX, mine had an aftermarket exhaust, air filter, 4 1" holes drilled in the lid of the air box, and was rejetted. A friend of mine owned a Suzuki and even with switching riders the Suzuki was faster. One the track, they're very comparable in handling, I personally prefered my EX on the track. The Suzuki felt more peppy coming out of the corners than the 400EX did, though.