Up until now I have been using a hacked around firmware in which I had changed the coil sequence to give greater torque when using tin-can unipolar stepper motors (by ensuring two coils were always powered at any given moment). Now I'm using some proper bipolar motors so I dug out my old JDM PIC programmer and flashed the chips with the last standard firmware.
I wired the motor coils up in series to give a coil resistance of 12.4Ohms per phase and a maximum current of 970mA. Well within the capabilities of the driver IC. The 'Rated Voltage' in the datasheet works out at setting the PWM duty to around 72% but the motors seem to run happily full power without getting hot.
At full power I can run the motor at up to 240 (PIC speed byte) with no load before the motor starts missing steps, and at 72% power up to 235
I haven't tested them for real on a machine but so far I am very impressed with these motors as they cost only £9.26 each when buying four + £11.97 postage
I tested all of this from a Python console:
reprap.openSerial('/dev/ttyUSB0', 19200, 60)
reprap.cartesian.x.active = True