Hi mate, I think its important to remember the FMC calculates its TOD prediction point based on lots of inputs, ie;
1) Cruise altitude
2) Cruise speed
3) E/D point
4) 'And where applicable, waypoint altitude and speed constraints
Based on these numbers, the aircraft should descend at the economy cruise speed (AKA VNAV Cruise Descent) based on your cost index number with T/L's in Idle/Hold (albeit with a little help using THR or SPD BRKS if your abv or blw path)..
Therefore, under normal circumstances, and winds permitting, the aircraft should never get even close to those VMO/MMO -16 (-11) speeds quoted in the FCOM.
Cheers.