Dan,
There is a considerable difference in servo centring under load. Digital servos should be much better, because they will apply full torque until they get to where they want to go, whereas analog servos apply torque that decreases rapidly as they approach the commanded position. Some are much better than others though.
Servormances does very good independent testing of servos. Not all servos have been tested, JR servos are under Graupner with different numbers, and it is in French. They test centring to 0.01 degree electronically:
http://www.aeroglide.net/2013/02/ser...-fevrier-2013/
I like the KSTs for the price too. Not as good as MKS, but at 1/3 the cost the KSTs are pretty good.
Kevin