Stepper motor ratings

Hi all,
As a follower of the elctronic leadscrew project I am busy
collecting 'bits' that I will need for the project. I have just aquired
an (apparently old) SLO-SYN stepper motor type HS50L - 1046D its the
size of a type 34 and is 135 mm long with 144 teps per rev and 6 wire 5
volts 4 amps. The problem is that the rating plate says 120 oz in.
The question is ......is this just a rating at a higher speed, or a
more conservative than modern ratings, since a current motor of this
size and current rating would have at least twice the torque rating. Or
is it just that the modern stepper motors have more output because of
better magnet systems ?

Regards Bob