OS X 10.9.2. As for the settings, it really depends on how detailed the scene is. Generally speaking, I think I see the greatest performance benefit from turning off realtime in the view preferences and the content browser. Those two settings appear to prevent the CPU from burning too much. If I do that, I can leave materials and engine settings high.
I wrote a little blog post that includes more detail here: piinecone — Unreal Engine 4 Performance on OSX