Rated power, rated current and rated rpm are the key parameters in the datasheet - these are
usually continuous ratings (unless the datasheet says otherwise). Sometimes you get values
for the best efficiency point (which is somewhat less than the rated power usually).
DC motors have a motor constant, measured in Nm/A or rads/s/V (one is the reciprocal of the
other), which will tell you how torque relates to current and speed relates to voltage. This is
a property of the number of turns in the windings, so a particular motor may have several
variants with different windings (and thus different motor constant), yet are identical mechanically.