stock busa should whip the zx12 all day. But it comes down to rider experience 100%. You need to learn to launch hard with an aggressive grip, and be HARD on that throttle in 1st, clutch bang shift into 2nd, and clutchless shift into 3rd (just give bike full throttle in second, let up about 20 percent and shift hard, and get back on it FAST! just wrist flick when you clutchless shift and you'll do it smooth)
It ALWAYS comes down to rider experience, and who is more comfortable running their bike hard. Wanna get better? launch hard out of every stoplight you come to. Go hard through 1st and 2nd, and you'll get alot better
The launch is everything. start letting the clutch out at about 5000+rpms and power hard. Once you feel the front tire coming about 2 inches off the ground out of the hole, you're getting it. g00s3 it!
Mike