Dual socket 1366.
My cad software vendor tells me to use a duo core instead of a quad, saying that most of the cad applications are single core compatible. Because I plan to use the machine for other softwares such as Photoshop, an FEM (Ansys) quad cores are also more appealing than a high speed duo core. My best bet seems to use a quad core with an LGA1156 socket because of the turbo boost that can bring an i7 such as an i870 (2.8 ghz) to 3.46 ghz. If I buy an LG1366(i900 series) I will not benefit from the turbo boost of the intel series 800 processors.