what plane are you using the servo on? IMHO, you don't normally feel a big difference in centering between a good analog servo and a digital unless your linkage rod are extremely stiff and your linkage is 100% slop free. And with regards to the torque thing, if you really need the torque and don't want to run the big battery pack, the 635hb or the 645mg is a good choice.

If you can afford it, go the lipo way.