My 5DII did get a fair bit of dust...
Thanks - helpful to know, if I go with a 5DII or III, dust will still need to be managed.
dont be afraid of cleaning the lpf yourself.
I do, often! That's the problem!

The 5DII and 5DIII have the same cleaning unit. The original 5D didn't have self-clean.
Thanks, and yes it was this point really that prompted my question. I have the original 5D, so I'm trying to get a feel for whether these cleaning units are effective. It's helpful to know that the 5DII and III both have the same cleaning unit.
I think I have a far greater tolerance for dust than most. I did not clean my 5D MK II for almost two years...
That's an interesting point and useful feedback, thanks. I guess it depends on the aperture that you shoot at, and also your own tolerance levels. Plus with a mark II it has the cleaning unit within it.
...the right sized swab and two drops of eclipse solution does the magic...
yes, sadly I am well versed with this technique!
There's also the question about
my technique: am always careful/quick as I can be when changing lenses, but more about the aperture I shoot with. With landscapes because I'll have my tripod with me I'm probably going for too narrow an aperture just so I get a good DOF. So any dust shows up on the sky. The upside is I'm pretty good with the RAW file corrections now!

The intent of my original question was an attempt to understand if one of my major bugbears would be solved or not by the advent of new technology. Based on the helpful feedback from this forum, (thanks everyone!!!) I'm concluding that the situation would definitely improve. Of couse as a hobbyist with no good business need to upgrade, I would say that wouldn't I?! I am looking for good excuses to make the leap from a MKI to a MKIII
