[Solved] Strange Performance from my HD 6870?

So, I just bought Battlefield 3 and began tweaking settings.

My setup is an i7-860 (2.8Ghz) core, one Sapphire HD 6870 (OC ~10%) and 8GB of DDR3 RAM.

At the following settings, I get these frame rates (checked in the same spot/direction):

1920 x 1080 - Everything Ultra (with no deferred AA) - 45 FPS
1920 x 1080 - Everything Low (with no deferred AA) - 48 FPS
640 x 480 - Everything Ultra (with no deferred AA) - 120 FPS

The fact that the FPS increases on a lower resolution tells me this isnt a processor bottleneck.
So, why do I see no difference in performance between Low and Ultra settings for shadows, textures, etc?

What game/s ?

Adding AA absolutely drops FPS, turning on Deferred AA at 1920 x 1080 drops my FPS to ~15 regardless of settings.

What's curious to me is that the detail levels of shadows, terrain, effects, etc. seem to have no impact on the card at all. Only AA (which I have to leave off) and resolution seem to change how strained the card is. I've never encountered this in other games, or at least not as extremely (low vs ultra shadows may only change FPS by 10 in Skyrim for example but in BF3 it literally changes nothing.)

Interesting, but I did watch a comparison when BF3 came out of the different settings, and the difference between low to high visually isn't as great as other games. Low settings still looked awfully nice to me, although I didn't actually try them myself. You could install MSI afterburner, and enable the overlay that shows your GPU utilization, and make sure it's at 99% when you compare both settings.

Best answer selected by elsnerj.