I would say get the 5DMKIII I moved from the 40D & 7D, the leap is huge.
Its a shame the 5DMKIII got such a bad reception when it was announced just because of price. I was blown away with it when it was announced, I couldn't have told Canon to create a more perfect camera for me. Its basically a full frame 40D with awesome IQ and noise performance with the best AF system Canon has to offer!
Dont be scare-mongered into believing that Canon cameras cant keep up. The banding and shadow issues are a non issue for 90% of shooting and if you know how to use a camera you wont run into these problems. It is more useful when you make a mess of an image and it needs some ridiculous recovery. Low light performance and noise is very very similar in real world application, 11.7EV is nothing to be sniffed at its more than enough range, 22mp is enough to create extremely detailed prints natively at A2 with no upscaling. The amount of people printing at A2 regularly I would say is quite small outside the professional realm.
In the 4 months I have been shooting with the 5DMKIII I have never come across the issue claimed by many, possibly because I expose my pictures properly. 6400ISO is a joy to use, its like 1000ISO on the 7D, a lifesaver. I shot these at 12800ISO recently as a test and they look fantastic, no banding very little noise and with minimal processing or effort.BMW F30 3 Series interior
, on FlickrBMW F30 3 Series interior, light console
, on FlickrBMW F30 3 Series interior, centre console climate control
, on FlickrBMW F30 3 Series interior, multifunction steering wheel
, on FlickrBMW F30 3 Series interior, iDrive screen
, on Flickr
This is my thread:http://www.canonrumors.com/forum/index.php?topic=13209.0
Couple of good articles recently on the forum that are worth looking athttp://www.arthurdomagala.com/blog/2012/04/dynamic-range-canon-dslrs-and-shadow-noise-dealing-with-it/http://www.dxomark.com/index.php/Publications/DxOMark-Reviews/Which-lenses-should-you-choose-for-your-Canon-EOS-5D-Mark-III/Canon-EOS-5D-Mark-III-vs.-Nikon-D800-Competition-is-closer-than-expected
The 5DMKIII is IMO one of the best cameras ever made for professionals. The IQ is stunning, its incredibly sharp, fantastic features, and the addition of the EF line up, there isnt really anything else I would want in the 5DMKIII. They have sold like hotcakes and most pros I know own them or want one. I dont know anyone who has switched to Nikon because of it mostly amateurs who dont use their cameras commercially.
But the D800 is a fantastic camera and it is cheaper but the files are just ridiculously large, you would not only have to invest in a new camera and lens system you would have to invest in a high end machine to edit them! Without even thinking about storage. If landscape is your thing I would say ye go for it the D800 is made for it, but the 5DMKIII is the best all round FF camera on the market and as the thread above suggests the sharpness is very close between them and much easier to get across the board with the Canon lenses.
But the D800 is slow for most other application and the file sizes are excessive for use and would need to be downsized in most cases. Fantastic for cropping, but where is the skill theres no point in composing lol! But if the best is all that will do then its a great camera but its not without its problems too. The IQ of a camera is important but the features and use of it are of equal importance, which is where the 5D is better IMO.
The 6D I wasn't sold on, the cameras performance is fantastic on par with the 5DMKIII in some cases better but if you are using primes wide open with only one cross point right in the middle focusing and recomposing will lead to focus shift. Would have been another perfect camera for a lot of people if they had put the 7D AF in it, in fact I would have bought one to go with my 5DMKIII instead I will get a second 5D.
I think coming from the 7D you will be blown away. I was pretty disappointed with the 7D not for its features or even high ISO performance but its IQ where it counts at 100-400 where I shoot primarily. The 5D is so clean here its amazing. You can play a waiting game for as long as you want but I don't see another 5D for 18-24 months. If you are really worried about DR then just bracket, then you will realise you don't need to.
Hope this helps