gravel, dirt, critters, cagers across the centerline, oil spots, tar snakes, not to mention those pesky traffic laws....there's a million reasons to ride at less than a track pace on the street. Dragging pegs either means you have poor body position and are leaning WAY farther than necessary or you're flying around the curves. Either way you're a disaster waiting to happen.
I ride a spirited pace on the street from time to time but I always try to leave myself enough of a cushion that if something unexpected comes up I have plenty of capability left to avoid it. Running at 9/10's means that if something unexpected comes up mid corner you are going to find yourself testing out how good your riding gear is the hard way.