Since the 5D Mark III came out there seems to be alot of people on this forum disappointed about it. Some say that Canon didn't listen to the users. Others are saying the Nikon D800 beats it on all specs.
I like alot of people who come here probably have invested a fair deal in Canon compatible lens and so at least for the moment are fairly stuck with Canon. It would be a major chance to move to Nikon at this stage and a major sell off of existing gear.
What I am wondering is are there people here with real world experience (as opposed to Spec knowledge) of the 5D Mark III and how does it compare to the 5D Mark II?
Is it a major improvement on the Mark II?
I haven't used a 5D3 yet but on paper the AF is way better than the 5D2.
The fps is much better as are the trigger response time and mirror blackout times.
The image review is better and other little UI things such as video/stills toggles and histogram outline, etc.
Video doesn't have aliasing and moire anymore and has at least 1.5 stops better SNR.
High ISO seems to be a little bit better, hard to say how much yet, high iso dr might be somewhat better maybe more improved than SNR, hard to say yet.
The downside is the MP count is basically the same and shockingly did nothing to improve low ISO dynamic range so it doesn't really take landscape-type stuff better than the 5D2.
It's certainly not worse, but after so many years you'd think it would do at least one thing better for landscapes.
They also crippled AutoISO yet once again, although it is less crippled than on the 5D2 where it's a total disaster, so that is better than the 5D2 but still bungled all the same.
They left out video basics like zebra stripes (which 5D2 can actually get with hacked firmware), focus peaking and a truly sharp 1.6x 2x2 c300-like sampled video mode (so still no crop video and still no super-crisp video). Not that the 5D2 had that but the 5D3 sure as heck should have.
If you don't care about body speed and AF or video then the 5D3 doens't offer much over the 5D2 though,if you do then it should be quite a bit better.
As for the D800:
The D800 probably has better metering, it has built-in flash and intervalometer, working autoISO, interchangeable focusing screens, it has a lot more MP for more detail and more reach, it has MUCH better low ISO dynamic range and similar high ISO performance until you start getting really high where it's high ISO shadows appear to become worse, especially ISO6400+. It has a little bit sharper video but it suffers from moire and aliasing and has maybe almost 2 stops worse SNR for video (granted most video is shot under better lighting where that doesn't matter as much, but when you do see that bear in the evening or shot some natural lit scene in dark lighting, etc. the 5D3 video would look a lot cleaner). It has only 4fps in FF mode, but it does have 5fps 25MP 1.2x crop mode and 1.5x crop 16MP mode (the latter with grip only though). As for AF, it is hard to say, some say it is better, some say it is worse, some say it is slower in poor lighting (although in super poor it does have an IR beam and can focus to some degree where 5D3 alone can't at all), who knows.