Current consumption of a stepper motor

Hi guys.

I am hoping you can help me with a question I have. I have just
finished a set of stepper motor drivers using a pic chip, an AND
gate chip and 4 of TIP120's . I have programmed the chip to be half
stepping only and and set up a simple PWM to limit the motor current
to 3.5 amps single phase at stand still (approx 5.9 amps 2 phase
exitation at stand still). I have a set of fast acting diodes
inbetween the motor and the driver. I have set the motor to start at
100 steps/sec and accelerate to 200 steps/sec after 2 seconds. The
motor is rated at 4.6 amps and is a size 34 unipolar motor. I have a
12v supply for each motor which is approximately 5 times the rated
motor voltage. I have connected an amp meter in the supply and am
reading 3.8 amps at 200 steps/sec.

Could anyone suggest what the current should be at this step rate so
that I can further tune the PWM section in the pic program because I
am not sure that the motor/ driver efficiency is good enough to
aviod loss steps.

Cheers Dave.