That problem is down to no heatsinks on the FET's for one thing.
That's not quite truth...Asrock P55-PRO has heatsink on mofets and Msi has to even if is small...

And even so for example Asrock VRM is in configuration 8+2 phases and 2 mofets per each phase.....Why sould't be these enough? Or 1.3v> the power consumption of 750/860 increase exponentialy? ....