My understanding is that driver-specific video card optimizations have the effect of shifting some load from GPU to CPU. In other words, the CPU spends time calculating optimizations which in turn reduce the GPU load.
If this is accurate, and if DX optimizations also have the effect of shifting load from GPU to CPU, then I wonder if it might be a useful config option to allow players the option to turn off or "scale back" the DX optimizations?
I base this partly on anecdotal evidence. Immediately before the patch, when my guild's camp/zone were already chock full of terraforming/buildings/players, I still had excellent framerate at my chosen (all minimal) settings. It was obvious that my graphics card had power to spare. However, since the "lag" patch several days ago, the framerate has dropped to an unplayable 1 to 3 FPS. Meanwhile the CPU fans have started to sound like a jet engine, and if I raise the Xsyon.exe process priority, the program maxes out every bit of available CPU time.
My suspicion is that turning DX optimizations OFF might help by shifting that load back to the GPU, which was handling the load just fine. Even if the DX optimizations result in lower overall load, if your system doesn't have the CPU time to perform those optimizations, while the GPU can handle the un-optimized load just fine, I would think the optimizations are just going to degrade performance.
Take with a grain of salt as I have only limited programming experience and never took a hardware course.