I've just checked the speed thing. The values from 0x42 to 0x4F set the speed for the motor - 0x41 doesn't do anything. So each wheel can be set to rotate at a different speed if required. Speed with 4F is about 0.4 revs/sec: 43 is about 1/4 that speed. The value is saved so it's probably safer to set the speed for each motor as part of the sequence. So for maximum forward movement, use 0xFF 0x4F 0x4F 0xFE 0xFE before the movement. For consistency it's probably best to clear the speed memory with 0x40 when done - this is what happens with the programming mode.