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I'm not convinced that the 6D is a significant improvement on the 5D2, especially if you're shooting RAW. LR4 does a great job of noise reduction at high iso.
5D3 is a decent upgrade for weddings if you need better AF and more FPS, otherwise stick with 5D2 and put the money into glass
I have a 6D, I had a 5D2, and I only shoot RAW.
If the OP is comfortable shooting a 5D2, the 6D will be an easy fit, offering significant improvements over the 5D2 in several areas.
Quieter shutter, better low light images, a big boost in ISO range, superior center point AF, and I have less of an inclination to chimp images and ETTR.
If the OP is looking for better AF performance, the 5D3 is a no-brainer as a replacement.
It's what I would have bought if I didn't already also have a 1Ds2 and a 1D3.