I have had my 7X12 CNC running with 187 OzIn Unipolar Vexta PK268-02A's in half-winding Bipolar mode for years. I finally replaced the Z motor with a 287 Bipolar Keling motor. About doubled the rapid to 1600 mm/min (although I have some sort of interference problem I recently discovered and a losing the occasional step, so I have halved the rapids for now, with reduced the problem about 10X.)
Mine has 2:1 belt reductions on both Axis. I did this more to avoid alignment hassles than for increased torque though. I really like having the X motor tuck under out of the way.
The swarf guard on Z and the enclosure are a real benefit for a CNC.
I replaced everything above the saddle. The stock X set up seriously limits the cross slide travel.
I wanted to fit a ball screw on X (zero backlash is more important on X than on Z), but haven't installed the little Roton screw I bought due lack of space under the cross slide for pair of nuts and anti backlash widget.
The cross slide currently has a 10x3mm trapezoid screw with two nuts, which I regularly need to adjust. Originally I put a 15x4 trapezoid screw with a Nylatron on Z. It now has a roton cheap rolled ball screw with a single nut. This was no real improvement over the Trapezoid set up.
I won't do any further upgrades to this lathe, as it is simply too small and flexible. The only reason I got it is lack of space. Still it has done good service and acted as a lathe, mill, drill press, bore grinder etc.
Take some time to set up/ repair the tail stock. They are truly crap on these lathes!
I burnt out my original DC motor and have a 1HP motor with VFD driving it now.