One more thing I didn't mention is that I built my computer for the specific purpose of rendering images as fast as possible to speed up production on the Prophecy comic.
I am running an 8-core FX processor over-clocked to 4.3 ghz, an ASUS sabertooth motherboard with the 990FX chipset, and 32g of corsair vengeance ddr3 ram, with Windows 7 professional.
The 8-core processor makes my render times extremely fast, but the ram determines how much geometry I can have in a scene. Once I get above 7 or so non-instanced figures, I start using more than 16g of ram.
So more ram = more figures in a render.