Have you noticed how much of each core is used? I have a dual core and Sins uses 50% of each. Maximum. Unless you set it a single core setting. It runs better that way.
The processor is an I7 Quad-core with dual threading so it runs sort of like an 8 core. The four that are getting the most use (1,3,5,7) usually run about 30%. Sometiimes the others get bumped to 5-10% but that could just be another processes getting handled.
The problem I would have if I set SoaSE to run on a single core is that it would only be 1.6GHz. That is low enough that I would probably see some problems.
Also, I haven't run a large map with multiple opponents yet.