i think running a modern square-frame stepper motor such as that with a unipolar board would result in less power output than a bipolar chopper board. the bipolar boards deliver more even amounts of current at different speed, the unipolar boards rely on huge 'ballast resistors' to maintain a costant current drain. This results in heat, and for big motors like these I think you may spend as much on these big resistors as you would on a good controller board.
The reason the unipolar boards seem to offer so much more power at a lower cost is that the electronics are alot simpler. The bipolar operation and constant current control require more inteligent control than a simple logic based unipolar board.
Most people would recomend geckos or similar for motors that size. www.geckodrive.com
xylotex, another popular driver are a bit small for that. What are you trying to move with these motors? That motor is big enough to move quite a big load. You may save alot of money by reconsidering your needs and looking at smaller steppers and appropriate driver boards.
People here seem to be using anything from 20-400oz/in motors with their zylotex boards and getting from 20-200IPM depending on their configurations. 1 gecko costs about $150. 3 xylotex boards cost about $150.
With geckos, and all their loyal customers, id imagine you get what you pay for. I will know soon.
Geckos max out at 7amps, i think. xylotex at 3.5 or 2.5... not positive.
Hope that helps