Ooooh, Ooooh! I want to get in the fight!
From my personal experience, the 5D has better image quality than my T2i(which has the same sensor as a 7D), especially at higher ISOs. Also, I don't think anyone should be shooting either sensor at higher than 1600, because they both look like uber crap beyond that.
The 5D and 7D have similar noise levels, but the 5D is ever so slightly better, and for some reason seems to retain more detail. The noise has a different character.
As far as it being quantifiable, when I look at comparisons online, they all seem to agree with the above, so I'm not sure where dtaylor is getting his info.
Check out DxO marks comparison. I know their overall ratings are meaningless, because no one can figure how on God's green earth they justify the weighting, but I think their testing is consistent for the individual tests and therefore, acceptable for comparison. http://www.dxomark.com/index.php/Cameras/Compare-Camera-Sensors/Compare-cameras-side-by-side/(appareil1)/645%7C0/(brand)/Canon/(appareil2)/619%7C0/(brand2)/Canon/(appareil3)/176%7C0/(brand3)/Canon
The 5D only loses in the dynamic range department at low ISO. And it's better than the 7D at ISO 800 and up.
Have a nice day everyone.