Hi there!
I was wondering if anyone knows anything about the Nvidia Geforce GTX 660 (not the Ti version), and it’s compatibility with the most recent version of Blender. My dilemma is that I have a Mac Pro, which is not compatible with many GPUs that are out there. I wanted to get rid of my old ATI, and get a new GPU, but I have yet to find the 660 in any benchmarks online. It seemed like the right price, and I’ve found some tutorials online about installing it, but I’m not quite ready to make the leap. I was wondering if there was anyone out there who could tell more more about this GPU’s performance and compatibility with Blender, if it is really worth the price, or anything along those lines. Thanks in advance, and hopefully I’ve made this understandable. 
I can’t speak for the GTX 660’s compatibility with OSX but I can tell you that it works fine with Blender. Not as good as any of the 5 series cards for Cycles GPU acceleration but does come with more RAM.
Ok, thanks! I was actually going back and forth between the 560 ti and the 660. I think you’ve just sealed the deal, I’m going for the 560 ti. Thanks for taking the time to reply, I really appreciate it!