The A3987 is good for up to 1.5A per phase/coil. But make sure that you do not exceed a Tj of 150C - proper heatsinking etc. I measured 9.8 Ohms per phase and you should limit current to about 0.6A (per the data sheet) with an appropriate sense resistor. For best performance I would drive the motor with at least 12V, preferably in the 18-24V range.