Blender viewport slow with many polygons, refuses to use gpu

I’m trying to push blender to see how many polygons I can put in the 3D viewport before it starts lagging. I’m doing this simply by subdividing a cube and rotating the view a bit. This ought to be a test on the gpu alone because that’s what renders the 3D view (just the area where you work & model, not the final image rendering). I have a GTX 275, but as soon as I reach ~1.5 million polygons, the viewport is reduced to rendering at about 1.5 fps. This is strange since I remember being able to go up to about 14 million polygons on my laptop w/ a GTS 360m before it got so slow. My RAM is only at 1.5/6 GB used, and my CPU (i7 920) is only 20% used when rotating. GPUZ says my gpu is also at only 18% load when rotating. Does anyone know why blender may be running so slowly, and refusing to use the full power of my gpu? Other applications are capable of using 100% of my processors, so there’s no hardware or driver flaw.

No ideas? :’(

have u tried VBO in the system panel in blender? it doubles the fps for me (nvidia m9600gt)