Ok just did the upgrade, they seemed to have made some changes to power management and have got rid of the Max CPU clock frequency. I can now fully confirm that the processor remains locked on the 0% processor frequency preset when I want it to!
By the way I'd encourage everyone to upgrade to 1709, it is the best improvement I have seen from any update and everything feels buttery smooth, even with my computer running at 1.2 GHz ! Exceptional.