I run 10.4 drivers with 11.2 caps and I dont experience micro stuttering. For one thing, trying to solve the fps dips down to 5fps is not the problem.. you need your overall framerate up. How can you play at 20fps? O.o
I run a 5970 and 5870 tri-fire, though Im not playing at your resolution.. Ive played crysis at a 3360x1050 and I know I couldnt play the game as smooth as I would have liked on max settings (AA full, etc). I can tell you now, any FPS or stuttering you experience IS because of your video card memory. Thats over 6million pixels changing constantly, the amount of memory for that is more than 1gb. My 1gb video memory is what is holding me back from even getting a 3rd monitor. I would rather have great framerates and stunning graphics versus "console" graphics with barely enough fps for smooth game play.
Try all kinds of different drivers starting back at 10.2. Thats what I did till you find what works best with your system.
It's not a vram issue. Read the thread goodness.