I think you could optimize your scene, by deleting history etc.
I have a particular scene where i have almost a miljon poly's in my scene and when i turn on the instances in the scene i have around the 50 miljon poly's, and still have a reasonable performance in the viewport.
I have a radeon x1950xtx 512 mb card (which i want to softmod into a firegl when i figure out how), so it's not exactly a high-end open GL card....