Yes the 2650 can take 6s... My dad has been using 6s and 2650kv for a year or more on his LX-1E. But Longevity MAY not be there... I say MAY because he just shattered the magnet in it YESTERDAY over a full year running with 0 maintenance. BUT it may have overheated from a Binding issue (Drivetrain) and melted/tore the epoxy/kevlar wrap causing the motor to fail at ~58,000 rpm. So there is no definate answer from me. But I say if you dont mind spending the $25 spare rotor fee then have at it! Its a Blast!
Oh BTW his never even got close to overheating before the binding issue. Even on 6s it topped at 120~