Hi John,
I have a Gorton 1-22 mill, a little bigger than the bridgeport. It has really old NEMA 42 Pacific Scientific motors with Geckos on X and Y and a big DC servo on the knee, Gecko drives all-around. I would avoid going with a knee-drive, it is slow, heavy, and it was pretty difficult retro-fitting a ball screw in there.... I run 80IPM rapids all around and can take heavy cuts at 30IPM no problem. Gecko's are superb stepper drives, I have a small preference for Vipers for servo (the preference gets bigger as the motor gets bigger :-))
Hope that helps,
Dustin
P.S- Direct drive on the steppers, .2in pitch ballscrews.