You probably want to consider more than the motors for your decision. What are you planning to do for your mechanical drive system? For a large machine like the one you are planning, screws are really not an option, so you will be limited to belts, chain, or rack and pinion (I might suggest ours...). This means you will likely want a 4 axis kit, with the two axes driving the gantry slaved together.
For high speed, a system that runs on a higher voltage is probably in order. For stepper motors, torque dies off as the motor rotates faster. This effect is always true, but you can extend the useable torque range by running at a higher voltage. The torque ratings on those motors are also fairly puny for a machine as large as the one you are planning.
A lot of people building plasmas have been happy with the Gecko G540 -- it supplies 4 axes, which you typically want so you can drive the gantry from both sides, and runs off of a 48V power supply quite nicely. It also features midband resonance compensation, and a robust interface to the parallel port. The driver advertised doesn't look too bad, but I doubt it is as bulletproof as anything from Gecko.