This is something I do daily, and to be honest, the complexity of the scene is pretty irrelevant. The CPU will always work at full while doing the render - It will just render it faster when its simple
This is *really* important when doing animations
The great thing with 3D rendering is the way it scales. Dual core quite literally means that the speed of rendering doubles (sub-system dependant of course!)
I couldn't believe how much difference a Opty 146 to core2 gave me in renders.
While they still aint quite real-time, they are getting there