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On my iMac I got 93fps on Mavericks then 88fps on Yosemite.

After the last couple of updates Yosemite is showing 92.25fps now.

So no major difference for me
 
I think that Apple doesn't optimize their drivers for the iMac 2011 models as they used to. Since Mavericks the GPU performance has gone downhill. A few months ago I installed Snow Leopard and it was (and still is) much faster than Mavericks and Yosemite.
 
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