I've been fiddling with the NVIDIA Control Panel and have tweaked things a little bit to where I get roughly the same performance with or without the d3dx9.dll. In this observation, I have noticed that when using the d3dx9.dll I am losing some particle and lighting effects. When I remove d3dx9.dll I see things such as little floating dust particles and light flare effects that the d3dx9.dll evidently cannot support.

Anyway, the NVIDIA Control Panel settings for performance I've come upon for Ultra mode involve the following changes:

• Multi-display/mixed-GPU acceleration: Single display performance mode
  
• Power management mode: Prefer maximum performance
  
• SLI rendering mode: 3-GPU Alternate frame rendering 2
  
• Vertical sync: Force on

Here's http://forums.nvidia.com/index.php?showtopic=158727 which has explanations of what some of these NVIDIA Control Panel settings mean. A few of the entries are a little out of date, but the main points are still there.

Disclaimer: While these work for me, they may not work for you at all. If you're still hosed after trying these, remember that game configuration is a journey with no real end. Please deal with your anger in a positive way and refrain from threadcrapping.