If you are serious about doing this project -- the servo which works best -will influence how successful you will be .
Go to the JR Servo site and look at the very small digital servos.
These have metal gears and being digital types, will have far better holding power than analog of greater torue rating. Not theory - fact.
(Has to do with on/off power inputs on digitals).
These servos , setup for maxixmum servo output rotation, will give you the most control power in the smallest lightest package.
Course - that's just my opinion.
We tested these smaller ones in Gas powered aerobatic models -on elevators --just to see what the probable failure rate would be.
They did not fail tho eventually the gears got a little loose in the second model we setup.
There are a few sizes to choose from -
If these are simply too large --look at the model 281 metal gear sub miniature servos .
Tho not digital ,they are quite strong.
We use these on our tiny electric acrobats.
Flying stabs are not anything new - they work well and as long as your setup does not "self excite" you should be fine.
Err on the stable side.
Whatever you do tho - set up geometry for max servo movement to required surface deflection. also max out travel adj in your TX --on JR that's 150%
any linkage slop or bending is deadly on these designs.