Liftmaster 3265 1/2hp
Premium Series
Chain Drive
The 1/2 HP motor is combined with the industrial-duty chain drive to provide steady performance and lifting power.

In Liftmaster's Premium series they have model 3275 which is the 3/4hp version of the 3265.
In the Elite series they have model 3595 which is suited best for heavy carriage doors and model 3575 which is another 3/4hp for the heavier doors.

Liftmaster 3800
24V DC Jackshaft
Provides ultra-quiet operation, along with variable speed smooth start and smooth stop.

Liftmaster has many varieties of garage door openers from a contractor series to a commercial grade.  Follow the link for more information or instructions/manuals.

http://www.liftmaster.com/consumerweb

Liftmaster 3280 1/2hp
Belt Drive
Features a solid-steel T-rail with automatic belt tensioner on the trolley, and an enhanced belt drive system for a more secure belt grip.

In Liftmaster's Elite series model 3850 1/2hp has the added benefit of the battery back-up system.  Model 3585 is the 3/4hp of the belt drives. It has 50% more power than they 1/2hp.