The torque will likely be enough for a mill drill.
A servo will have an almost flat line from zero RPM to its rated RPM for torque, maybe dipping slightly as the RPM reaches the rated speed.
As for servo drives have a look at this page
http://www.thecubestudio.com/ServoDriveReview.htmI have both Steppers and AC Servos on the machines I have and each have their place. For a mill or lathe of a reasonable size I would now not use anything other than an AC Servo but on the coil winder I made a servo would be overkill although the noise of the steppers is a bit annoying at times
I also have steppers on the Bridgeport and although I have no problems with them as far as accuracy and losing steps they are slow, particularly on acceleration compared to the AC Servos I use on the other mill and the lathe.
Word of warning though, often places that sell the servos for hobby use quote their peak output, so you have to take that into account. Much better to find what their rated output is and work with that.
Hood