ORIGINAL: B EXTREME
The hitec 225 don't really seem to have centering problem. As far as i can see they seem to be a good sevo for 424. I run the nylon gear version on the ruddervators in my viper, keep the the arms short and give yourself the greatest mechical advantage possible and they hit the mark every time.
Small
lightweight
Plenty of torque
no backlash
...GOOD SERVO
I've written this before but maybe it bears repeating. Many times the centering problems with 225 servos can be traced to a tight iron/ oilite bushing at the base of the output gear. These servos have a ball bearing on top of the gear / the bushing on the bottom. Replace that bushing with another ball bearing from an old servo or a new one from some place like Boca and you will be amazed how much better they center. These are good rugged servos that offer quite acceptable centering if these bushings are not too tight. The ball bearing is less than $5.00 new if you go that route.