No, it's not. The problem that Mack is having is due to the lack of VRAM. He is using 2 670s with 2GB of GDDR5 each. That equates to 4GB spread across a ridiculous resolution. If you get 2 of the 4GB 670's you will have 8GB of VRAM. This will allow you to push higher resolutions without frame-rate drop. If you want better results however, I would go with two GHz Edition 7970's. they are about the same price as the 4GB 670s but have been shown in gaming to be higher performing. Also 7970s can be overclocked like there is no tomorrow.
Ah okay, thanks. And I was planning on 4GB. And AMD is not an option for me. When you make computers and put OSX on it, you need to be careful with hardware, because OSX doesn't like some hardware, including AMD 7XXX Series. NVIDIA basically runs native to OSX.