Performance Level issues with GTX 660 ti

I’m experiencing performance level issues with my GTX 660 ti card. The card stays at performance level 2 (705 MHz gpu clock, 3004 Mhz memory clock) at all times on my linux desktop. At first I thought it might be related to the desktop environment used (compositioning etc.), but the problem persists, even with plain X.
One way to get the card to clock down is to remove the second screen from the twinview setup. However : I ran Diablo 3 the other day with wine and after leaving the card switched the performance level as expected (pl. 0: 324/324 MHz), even in twinview mode.
What might trigger this change ? any ideas for a quick workaround that would work at boot time (as opposed to running D3 every time to get the card to clock down) ?

My Setup : Gigabyte 660 Ti, nvidia-drivers 325.15, Openbox desktop
The issue does not appear when using windows 7.

Bump… Driver version is 331.20 now. happens regardless of distro (tested Gentoo, Ubuntu, SteamOS beta). Running D3 with wine still works as a (horrible) workaround.