Dual motor drives for the gantry work very well if the gantry and gantry supports are stiff and well connected together. Mach3 and EMC2 both can slave the two motors together in software. It is steadily becoming the more popular way to drive a moving gantry machine. I'm using it on both a dual rack and pinion drive machine and a machine using dual ACME screw drive.
You have twice the torque pushing or pulling the gantry. Cutting near one side of the machine doesn't cause the racking problems that one motor driving from the center of the table has had.
CarveOne
CarveOne
http://www.carveonecncwoodcraft.com