dont lower or stretch your bike, yes it will be a 1/1000 of a second faster in the quarter mile, yes you will launch harder, and sure there are benefits, but you'll commit your bike to the 1/4 mile track only, and everywhere else your bike is going to suck
leave it stock height. Lowering it is asking for trouble in the turns and everyday riding, especially 2 up. It wont corner or handle like it was deisigned.
Quarter mile times arent everything. Being able to corner with clearance and handle bumps on the road are much more important than simply going 9.2 instead of 9.4 in the quarter mile. Lets not even get into resale value, you're bike wont be worth sh*t with that done, people will assume it's been ragged out and trashed and wont want it
Mike