DX10 allows a lot more calculations to be handled by the GPU so the CPU can send less information for the same end result. However, games in DX10 are going to utilise these advantages as much as they can, so you still need more CPU for more performance.
The real issue is that a 2700 MHz X2 is fast enough for anything out there now. Converting to Intel will see a performance increase, but if you are using an 8800 you are most likely cranking the eye candy which will greatly reduce the advantage of a different CPU. We should at least wait for true multi threaders like Crysis to be tested for a while before we are forced to switch, and by then AMD may have a quad as well, bringing down all of the prices.
From
http://www.gamespot.com/features/6143883/p-4.html:
"DirectX 10 will increase game performance by as much as six to eight times. Much of that will be accomplished with smarter resource management, improving API and driver efficiencies, and moving more work from the CPU to the GPU. "The entire API and pipeline have been redesigned from the ground-up to maximize performance, and minimize CPU and bandwidth overhead," according to Microsoft. Furthermore, "The idea behind D3D10 is to maximize what the GPU can do without CPU interaction, and when the CPU is needed it?s a fast, streamlined, pipeline-able operation." Giving the GPU more efficient ways to write and access data will reduce CPU overhead costs by keeping more of the work on the video card.
Here's a list of several new Direct3D 10 performance improvements GameSpot was able to wrestle out of the DirectX 10 team:
New constant buffers maximize efficiency of sending shader constant data (light positions, material information, etc.) to the GPU by eliminating redundancy and massively reducing the number of calls to the runtime and driver. New state objects significantly reduce the amount of API calls and bandwidth, tracking, mapping, and validation overhead needed in the runtime and driver to change GPU device state.
Texture arrays enable the GPU to swap materials on-the-fly without having to swap those textures from the CPU.
Resource views enable super-fast binding of resources to the pipeline by informing the system early-on about its intended use. This also vastly reduces the cost of hazard-tracking and validation.
Predicated rendering allows draw calls to be automatically deactivated based on the results of previous rendering - without any CPU interaction. This enables rapid occlusion culling to avoid rendering objects that aren?t visible.
Shader Model 4.0 provides a more robust instruction set with capabilities like integer and bitwise instructions, enabling more work to be transferred to the GPU.
The D3D runtime itself has been completely refactored to maximize performance and configurability by the application.
It remains to be seen just how well actual DX10 graphics hardware will be able to handle the additional work, but we've seen in the past that ATI and Nvidia have been able to deliver whenever games have shifted work from the CPU to the GPU."