Digital servos are x10 faster then analog. Hooli for sure knows more then me as I'm just getting started here, so please correct me if I'm wrong. But I believe analog servos can only cycle 30 times a second where as digital servos can cycle 300-400 times a second with the gyro. I do believe you need a gyro that is capable of working with a digital servo (maybe they all work with digital/analog, but I don't think so). So you get a much greater control over your position with digital.
As for the servo, I don't necessary need a super fast servo. I mean seriously, how fast do we really flick our bikes back and forth, not that fast. What is probably most important as you mentioned is holding torque. The ones I have tried in the past were small and just wouldn't cut it. This one is much larger and we will see how it does.
I did get my mounts in the mail last night and I will be needing to go to the hardware store now to gather a few things to fab up for the next trial.

can't wait!