Yamaha builds very rapid 600cc fours going all the way back to the '84 FJ600, which, if you're interested in a little genealogy lesson, begat the '86 FZR600 and the '94 YZF600. Four years later, the YZF was soft enough around the edges to earn Best 600 GT in our August '98 issue. Brand-Y got serious again in '99, catching the rest of Japan Inc. on their corporate heels with the first YZF-R6. While initial rumors of 120 horsepower in a sub-400-pound package never materialized, the strategically recast R6 that materialized in the spring of '03 weighed an astounding 415 lbs. wet and made 105 horses at 12,750 rpm-11 lbs. and 9 bhp ahead of the '02 version. Credit a new aluminum frame and wheels for much of the weight loss. Factor in a stubby, 54.3-inch wheelbase and steering inputs are essentially instantaneous.