It's not the same sensor. Canon's web site describes it as a new design.
Of course it's not the same - it's 20 MP, not 22 MP. But if it uses the same production technologies found in the 5DIII and 5DII, the IQ should only be marginally different, if at all.
+1 as Neuro stated (20MP vs 22MP)
Prior to my 5D III, I owned & used 40D, 60D, 7D, 5D II and tested and owned a lot of lenses. My comments are based on hand-on-experience, not what I heard and read on internet and interpret to this forum.
How often to hear people give advices or comments on FF gear, while they shooting crop. Reality is.... you get for what you pay for.
I can see another post with title like this soon: 6D + 24-70 f4 IS is out perform 5D III + 24-70 f2.8 II