Ok i've figured it out.
HAGS made zero difference BTW.
The key is Nvidia power management in control panel. Set this for MPV player (i've not got MPC working yet) not globally:

As soon as you set this to high the playback is smooth at x3 however look at the power useage vs x2. Perhaps I can play around to find the lowest possible settings to run at 3x's when I have some more time:
x3 (Maximum Performance)

x2 (Normal Power usage)

My SVP settings are as follows:

x4 does not work.
So I guess pay your money take your choice.
Edit I've played around with this now and get power usage down somewhat. I can't go any lower on the core than 2015mhz a or else the voltage jumps back up to 1.05v for some reason? I've also downclocked the memory.
