AF upgrade for 5DII - 6D or 5DIII

I just came back from a trip to Asia and I have finally had it with the AF on the 5DII in low light (6400 ISO type low light). So can I save some $ by getting 6D or do I just need to get the 5DIII. I am thinking 5DIII at this point but want to check before committing. Thanks

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What camera do I have? I rather you look at my photos www.flickr.com/photos/gavinz