You keep being very negative about the 5D3. While you may be expressing a sincerely held opinion you are going to struggle to convince many that your opinion is well founded. There are so many excellent photographs taken with the 5D3. I have seen images taken with Nikons, some of them outstanding, and I have seen and taken images with Canon. What I have never seen is anything that convinces me that either has a fatal fault or weakness.
I wouldn't call it a fatal fault. It's just an excessively annoying fault. My 450D had it. I skipped the 5D II because of it. The 7D has it, although not as bad. The 5D III has it, about as bad as the 5D II (despite the decent number of years difference between them.) So, no, not a "fatal" fault. An ugly, nasty, frustratingly annoying fault, yes.
Don't get me wrong. Some of the excellent images I have seen were yours. (I think your astro photography is excellent) But your logic is not too hot. To say you have been frustrated by Canon for over 6 years but its only the 5D3 just isn't logical. I know that you can say you only said you were dissatisfied with the 5D3 and frustrated for years. But hey we both know that's just wriggling.
Its a shame you have been subjected to quite so much agro. But I think you have rather asked for it by the way you have expressed yourself so strongly without taking much notice of many valid points that have been raised.
Eh, I knew what this community was like when I voiced my opinion. To be frank, I never really expected anything else. We crucify anything DR related, PARTICULARLY DXO (although, I still think DXO is asking for it...they need to stop being so obscure about their methodologies and weighting, and stop posting ludicrous lens test comparisons.) Anyway, people are what they are...and here they like to crush any mention of DR differences between Canon and the competition.
As for the rest...I was frustrated with the 450D read noise, that was my first DSLR. I did not like the 7D noise either, and was frustrated with it for over a year until I got the whole Topaz filter collection for about $130. DeNoise 5's debanding works extremely well on the 7D, since it has a very regular 8-column repetition. I can just set the band width to 8, and DeNoise 5 completely eliminates it. The low read noise then means the remaining random noise cleans up well. So, I was frustrated with the 7D until DeNoise came along.
Part of my frustration with the 5D III is it seems to have largely random banding. Some bands are very thin, some are quite fat. DeNoise 5 cleans up some bands, and not others. I can run multiple passes, but then I'm eating away at detail. So, the tools I used to use to deal with banding don't work nearly as well or at all with the 5D III. The color noise is also quite bad...however last night I found a new "smoothness" slider in LR 5's color NR that seems to deal with the larger-scale blotchiness...so that may help with the issue. (Crosses fingers.)
Anyway, I had frustrations with Canon read noise a long time ago. I skipped the 5D II because of it's read noise (at the time, the rumors here were that the 5D III would hit around 28mp and have improved DR...so I waited.) I'm harping on the 5D III because it's one of Canon's newest high resolution full frame sensors. It's their current technology. The 6D performs remarkably better at high ISO...and statistically given it's read noise levels, it should perform similarly at low ISO (I don't know if there are any low ISO comparisons between those two cameras...everyone focuses on the high ISO differences.) So, my reasoning is logical. I've been WAITING a long time for Canon to fix their banding issues...and the camera I have in hand right now is the 5D III.