Here is an idea: could it be that a PERFECTLY rigged stab linkage is OK with the recommended servos, but if the linkage is a bit out of rig, then you need a bigger servo? Seems to me that it would be good insurance to put in an 8411 or similar just for the peace of mind.

It also seems to me that Mr. Gladwin is very much worth listening to. He has tons of real world experience, and whether he is right or wrong. deserves respect.