Personally, I just can't see the economy in using 2-rudder servos and 2-elevator servos. I installed a HiTec MG125 aileron servo into the horizontal stab for the elevator. I'm driving the rudders with a Central Hobbies, carbon fiber connecting rod pushed by a JR standard servo mounted inboard on the starboard tail boom. If I could figure out how to couple the nose gear to these, I'd dump that servo too. More servos=more current drain on the battery pack, more weight, more wiring and more headaches, (IMO, of course).
While I am all for weight savings, reducing the amount of servos in this example doesn't really save any weight. A Hitec HS-85BB servo weighs .67 oz. each, 1.34 oz. per pair. One standard servo on either the starboard or port side for rudders weighs more than a pair of HS-85BB,s but does save some money. Modifying the stab to accommodate an HS-125MG and routing the wire is a bit of a headache. The single HS-125MG weighs .84 oz. as compared to (2) HS-85BB at 1.34 oz. but the HS-125MG is 6" farther behind the CG so I'm not so sure there is much if any weight savings there either. I personally wouldn't trust a single HS-125MG to handle the elevator as it is a mini servo and has the same torque rating as a single HS-85BB. I do agree with keeping the powerplant on the light side, seems the OS .55AX is a pretty good choice for the money.