RE: KMP F-7F Tigercat
There are 2 servos for the elevator (one per half) and the requested torque is not that high, so 2 x 4kg/cm is plenty enough. If you need one with more power it will be the rudder one, but 6kg/cm should be enough. Personally, as I will fly electric, I will go with Hitec 5245MG on all control surfaces, but the rudder where I don't what I will install.