For our applications, most specs aren't important. Unless you are working in a tight space, the larger size is fine and usually offer more torque, etc for the price. Steel gears and all that don't come into play with our stuff since the things we use them for: recoil, elevation shoudn't need an overabundance of power, it's not like you're trying to pull a rudder against 100 mph wind resistance via a 6 foot cable. They're all engineered to plug into a receiver and handle voltages that the Rx does, so don't worry about our 7.2.

To run the traverse and elevation in the SU-100, I used the Futaba servos (2003s) that came with the Attack Tx/Rx about 15 years ago, but I generally go with them for anything since they are reliable and inexpensive. I'm pretty sure you can get them for under $15.