I have converted my mill which is an IH clone from Machine Tools Warehouse.
I used 50 oz-in continuous torque servos for my build (nema 23 frame) and I'm using a 4:1 reduction drive on the x and y axis, 5:1 on z. This results in quite healthy accelerations (70in/s^2) with my 50lb vice on the table, (ie under 0.05 seconds to 200ipm velocity), less accell and velocity on z (~50in/s^2 and ~100ipm due to variable gib tightness at top and bottom of travel)
I can achieve 200ipm (x-y) but its at the max for my setup. If you want to achieve these numbers regulary then what I've done is the bare minimum and its best to add some margin to it (but not too much if $ is a factor).
For the DC brushed servos the next step up is 100oz in I think. Another option might be looking at the kit from here DMM tech Pricing - guys in the router forum have used it and seem pleased. I would like to try but the max voltage is below my current power supply so I'd need a seperate one just to try...maybe later when I do my lathe. If you need to buy all your parts then 1 stop shopping might make good sense...