Images off my 1DMKIV are simply stunning, especially in studio at 100 iso and they were beautiful when i needed 6400. I have a 5D2, i think its great as well. I don't shoot in servo much because ive always got a flash on my camera at weddings but when i shot in servo i have not experienced any locking issues however i know other have. Gonna push this camera a bit in the spring and find out where the limitations are at with servo.
That being said, my opinion is that the 1DMKIV is the best camera ive used to date. I locks everyplace i put it and the images and IQ is the best in canons line up right now.
Bought the MKIV in anticipation of this release because it does so many things that i want my cameras to do. I love the 1.3 crop factor and the 35L on this thing blows me away. I do weddings and portrait work to pay the bills and i play around and shoot some wildlife and sports for my playtime. so the MKIV does it all for me. I cant tell yet but from what i see being posted,, MKIV files and 5D3 files look dam close at noise levels and IQ. I think they are both very usable at 6400-8000.
For me, MKIV was the best choice, but we also have a 5D2 and a MKIII. I want my next camera to be the 1Dx, pending on what its going to be on the market for. Im doing nothing until i see tests from digital picture and DP review after 1Dx and 5D3 are tested and conclusions are made. But either way i feel like i have it all with what i have and it could get a lot better depending on how these cameras test out. I could easily go 5D3 if it tests great. But if a 1Dx blows the 5D3 away and its another stop better in iso performance and a few steps better in IQ,,,,thats the way i will go,,,IF it stays below the 7K pricepoint.