Choosing a Gaming CPU: Single + Multi-GPU at 1440p, April 2013

One question when building or upgrading a gaming system is of which CPU to choose - does it matter if I have a quad core from Intel, or a quad module from AMD? Perhaps something simpler will do the trick, and I can spend the difference on the GPU. What if you are running a multi-GPU setup, does the CPU have a bigger effect? This was the question I set out to help answer.