Stepper current - how bad is underdriving a motor?

I just acquired a NEMA42 stepper,

840 oz-in,
1.45V
15.2amps !!

I was wondering how much torque I
sould expect out of it when running
on a Gecko at 7A? I do know that
whatever torque I get will stay
there to a rather high speed, thanks
to the very low voltage.

John Kasunich