Flats are even worse on a bike cause you cant repair them(if you are sane) like a car tire. I recently had to replace my rear tire cause of a screw. HIGHREVVER, was your front stock a 208 or 218? I had Dunlop 218s stock on my bike and replaced the rear with a qualifier and left the front stock. One of the guys at my dealership said taking turns aggressively at higher speeds with the diff in compounds, heat up time, temp and tread will cause the front to wash out because it wont hold at the same angles and speed as the qualifier. I was skeptic........ til it happened two days later. I wasnt going fast, thank god but I had been on it hard for a little while and that was all it took for me to believe him and get a qualifier put on the front the next day. Mismatched tires may function ok if they are both aftermarket but keep in mind stock tires are harder, heat up slower and are almost never used for competition because of this. As far as going above 80mph on mismatched tires, nothing is required of the tires other than to hold air to go in a straight line. I assure you if you corner hard above 80 with mismatch you are asking for trouble. Just my opinion though as I am sure someone out there has done it. I also know people who have lived through a bad crash....doesnt mean I wanna do it.