Yeah, Test ride it.
Thts the best way to judge the performance of a bike. Besides, Access also has the largest of all the engines in the bikes mentioned here along with the flyte. Its a 125cc scoot..so yeah, it'll definitely feel peppier than the rest of the bikes, but i guess, the extra 'cc' will definitely affect the mileage adversely. It may give lesser mileage than a well maintained activa..
It wud be better if u surf around the xbhp/tbhp forums and get in touch with those who have bought the access, to get an idea of the real world mileage tht they may be getting.