I dunno where you got the DOM from, but the 757's i fly are nearer 60 tonnes DOM rather than 62 Tonnes.
I've never seen a 757 MZFM restricted on any thing i've done. Max TOW, occasionally, on some of the lighter (108 tonnes) 75's, but not ZFM. In fact i've done quite a few flights to Africa where the limitation has been that the hold is physically full - we've still got weight to play with but the guys cannot squeeze anything else in!
The 757 has got so much take off and climb performance that even on short runways, unless its a very hot day, Structural take off mass rules the day, rather than performance limited.