Brooke,

I just finished my Skybolt, with a O.S. FS-91 four stroke. I used the Futaba R168DF, S3004 servos w/ 6 volt battery, @ 6v you have 57 ounce-inches of tork with no problms.

Yes you can use the S3010 servos instead, I'm running the S3010 in my Showtime @ 6 volts because of the size of the surfaces and I wanted the higher tork and speed.

To answer your question "why one is better than the other", the way I see it , it really comes down to operating speed (go with 6.0V), no load stall torque, motor type (coreless or 3 Pole Ferrite), bearing type (ball bearing is better) and last but not least gear type (nylon or metal)..

Like a lot of bi planes mine was a bit tail heavy. So test fit your radio gear , smoke system and battery before you deside on a location. Your going to what to get as much weight up towards the nose as possible. Using the recommended CG I needed to add about a once of lead on the firewall.