Sanity check for max motor torque
Technically speaking, if you could dump 4285A in that motor steady state at 30V without melting it to slag, then yes that is the stall torque you'd get. 

Dumping 128,571 watts into that motor might have some amusing results, but the end result won't be an exciting 81 Nm of torque. Use the rated motor current from the spec sheet instead.  

Also, it is useful to note that with an ideal sensorless six step controller, you won't even be able to get the rated stall torque. In a practical setting, you need a sensored BLDC driver for high torques at low (to zero) speeds.