First off why are you doing the upgrade? Why do you need a different body?
I love the 85 and the 135L I own and hope to use them more. I have also shot 5Dc and 5D2's and love the images they produce.
In terms of cleaness, likely ISO 4300 on the 5D3. The 40D at ISO 800 would be as clean as the 5DII at ISO 2133 (this has been tested in lab conditions)
I imagined it would be better - thanks for confirming it.
I would get the upcoming Tamron 24-70mmm f/2.8 VC lens. That's the best of both worlds, image stabilization, and f/2.8. It's also reported to be very sharp.
The new Tamron does indeed seem intriguing - any word on when it will be available?
The 24-105mm f/4.0 IS would look cleaner on the 5D3 than the 17-55mm f/2.8 on the 40D, if the DOF is the same. However they would be about equal with the 5D2, with only a slight improvement.
So, it would appear that the 24-105 kit lens would be a great addition to a new 5D2 or 5D3. Thanks for your insight.