I'm hoping someone more knowledgeable than I will chime in here. i have a couple of Eagle EA-550s and they start at 200 rpms. No ramp up, no slow start - BAM, instantly 200 rpms. I've read things that lead me to think the "other" style of servo, with a knob and it looks more like a clutch motor, will go much slower but at the expense of losing torque.
One of my EA-550s is on a machine with a 3:1 speed reducer so my "instant on" speed at the needle is only about 52 stitches per minute. Actual, counted speed.