I am waiting for the 2013 refresh. My 2006 Mac Pro 3.0 Ghz, 8 core is still running pretty smooth. But, I need the power of the next gen. Mac Pro's Which will only happen when Apple refreshes their Mac Pro line in 2013.
I would recommend you wait for the 2013 Mac Pro models.
Your budget, and the pricing of the new 2013 Mac Pro will be something you need to factor into your decision. For now, there is no info. on 2013 Mac Pro specs, pricing, or when they will be released.
So... If you are in a rush, go for the latest 2012 models, otherwise, waiting has its benefits.