Tenson Jonathan's right on all counts here. I gave you the options he's giving you specifics about the rotating nut. If your wise you'll go with the rotating nuts at this length for best speeds verse's cost's.
The rotating nut will give you best of both worlds and save you some money.

The other reason for not using 1 drive with 2 motors is that if the pulse timing doesn't get to each motor at exactly the same time then you will slowly drift either infront or behind on 1 axis so all in all it's a lose lose situation and at best you'll be inaccurate and worst be letting out the magic smoke. . . Your choice.!!