On my current Laser I am using 5 Hitec 425bb's and one Hitec HS300 (throttle) with a 6v 700mah battery. No problem.
On my first Laser I used 425bb's on ailerons, 605's on elevator, 545MG on rudder and s3003 on throttle also with 6v battery. Also no problems, the point is standard servos are just fine in this plane.