Mac Pro 4.1 CPU upgrade

I'm actually looking for faster render times in Maya 2013. As I get told the render time is due to the performance of the CPU, I'd like to upgrade since my render times are kinda slow actually.

So, considering I have the original CPU that came with the Mac Pro 4.1 (2 Quad-Core Intel Xeon 2,26GHz), what's the options that I have? Also, I'm working 80% of the time in BootCamp Windows 7, don't know if it can change things?

And last question, if I upgrade my CPU, would I have to change...

Mac Pro 4.1 CPU upgrade