Certainly the earlier MTH HO locomotives tested by MR were noted for needing a lot of starting voltage in DC, and this had the effect of clipping or limiting the top end speed. It would not be a problem for lighter and slower consists, but for fast freight or passenger/meat/silk trains, and heavier ones at that, it would be impossible to get limited speeds out of them for power supplies that top out near 12-14 volts. For those that can provide 16 volts or a bit more, you probably wouldn't find it so limiting.