Sprockets make a difference big time dropping a tooth in the font willgive you more torque. Which in turn means faster acceleration off the line and the ability to lift the front wheel so much more easily. However there is a down fall to dropping down a tooth size your top end will fall off by about 5-7%.
Sprockets are cake to change. Providing you have all the equipment to do so. They can be changed out in about 20 minutes after you get the rear tire off the ground.
if i have time i might be doing it ton, not sure yet. and of course most deff i will let u guys no the out come. and all is true above. i will be loosing top end but picking up gobs of low end and the front wheel is goin to want to come up. but i figured we have 636's i had mine at 160 already no prob with plenty to go. looseing 7 or even 10 percent of top speed don't bother me considering your going to get there alot quicker and we all no the 636 goes more then 160 :mfclap