The best time on my trek 4300 with default bontrager knobbies for 200 on mysore highway, was ~8.5 hrs
IMO, the brevets can be done on any bike.... We even saw Amar ride a singlespeed Atlas at an awesome pace on the mandya brevet, beating many roadies(myself included) to the finish
But, the longer the ride gets, the better a rider u need to be, to maintain a good speed