Larry,
I like the single servo better that the dual. the gears have a bigger mesh and are stronger.
this are the specs of the Rhino servo at 6V.
The strongest Multiplex servo. Metal gears with final gear made of steel, triple ball bearing. Servo disk with alloy reinforcement ring.

Data @ 6 Volt
power supply: 4-5 cells
torque: 250 Ncm
stall torque: 225 Ncm
speed: 0,10 sec/40°
weight: 175 p
dimensions: 59x29x55 mm

Holeshot,
in-line hubs have faster and linear response, off-set give you a good entry with a big push out of the corners. I'll post a pics of my front end tonight..