Tried using any commandline parameter ? I suggest "-availablevidmem 5.0" without the brackets... and also, try switching down your resolution, you'll hardly feel a difference.
What does that command line do exactly?
Because after adding it, look at my Resources Available. Which was previously 495Mb

And Leon, I have the exact same graphics card, this is how I have my settings, seems to work perfectly fine.
And heres my commandline settings.
-memrestrict 314572800
-noprecache
-availablevidmem 5.0That last line "-availablevidmem 5.0" is what Niko said, after adding it, for some reason I have a massive increase in Resources which before was 495MB like yours.