So, your X/Y steppers, with a 5mm-pitch ballscrew:
425 oz. in @ 0 RPM (continuous holding torque)
127 oz. in @ 300 RPM continous, = 60 inches-per-minute
42 oz. in @ 900 RPM continuous, = 180 inches-per-minute
My Globe motors with 2.8:1 timing belt reduction make 60 oz.in. at 1000 RPM so they may be ok. Torque also goes up the slower they turn. I'll probably crunch some more numbers tonight.
Oh yea, one other question...
Can this mill do really fast feedrates for G00 rapid movements? If so, how fast?
How has the accuracy been with your 5" vice?