At the mo I have a 550d and a 60d. my lenses are 17-35 2,8L, 24-80 2,8L, 70-200 2,8L, 100-400 4,5-5,4L sigma 150 2,8 and looking for the canon 50 1,2. The obvious next step is a FF Body. My main interest is Large Landscape panoramas and macro. As I also do Photographic Safari guiding I also do a fair amount of wildlife and Birding. Here the APS-C sensor are fine. My actual question now, how good is the AV of the 6d in comparison to the 5d mkII when it comes to macro work and or wildlife. I always read the AF is only one crosstype, bad tracking ect. the lowlight abilities pull me towards the 6d the weather seal to 5d.
For Landscape and Macro work there is very little difference between these two. That is assuming you are shooting RAW and manually focusing as is often the case for those two types of photography. The resolution difference is only about 2.4% in favor of the older 5D Mark II.
At ISO 1600 and below the differences in sensor image quality are minimal. Above ISO 1600 the 6D has a little better dynamic range than the 5D II. But as is the case with pretty much every digital camera when dynamic range at high ISO is compared to the dynamic range at lower ISO settings of course neither camera has near the same dynamic range at high ISO. A direct comparison of sensor performance can be seen at DxO Mark. As always, click 'Measurements' and then the various tabs for 'sensitivity', 'SNR 18%', 'dynamic range', etc. to see the measured data.
Improvements made to Canon's (or other parties) RAW conversion engine since the release of the 5DII can be applied to RAW images from either camera. If for some reason you desire to save your files converted in camera as JPEGs the 6D presumably has a little better JPEG performance. The same is true of the auto focus performance of both cameras. The 6D has a little better AF performance than tbe 5DII but neither camera approaches the advanced focus system of the 1D X or the 5D III or even the 7D. Functionally the AF systems are very similar in terms of number of AF points and the way they can be set up by the shooter.
The 5DII has both a higher maximum shutter speed (1/8000 vs. 1/4000) and flash sync speed (1/200 vs. 1/180). This points to a faster curtain transit time for the shutter in the 5DII. This could affect the way images of fast moving objects appear since the total time needed to take the shot is the time it takes the narrow slit between the curtains to transit the sensor, not the time any particular spot on the sensor is exposed as the slit between curtains moves across the sensor. The 5DII also has a higher shutter durability rating (150K vs. 100K shutter actuations).
The main differences between the 6D and the 5D II are in areas that do not directly affect image quality: WiFi and GPS capability for the 6D, SD card vs. CF card (some folks prefer one or the other), lighter/smaller vs. larger/heavier (some folks prefer one or the other). The LCD screens are the same size but the 6D LCD has about 13% more pixels (just remember all back of camera LCD screens lie like politicians anyway). The 6D is more flexible in terms of Auto Exposure Bracketing with up to 7 frames at +/-5EV while the 5DII is limited to 3 frames at +/-2EV. The range of exposure compensation for the 6D is 5EV vs. 3EV for the 5DII. Of course any of the exposure values available using AEB or EC with the 6D (plus those that use Tv greater than 1/4000) are available in the 5DII using Manual exposure mode.
When you asked about how good the "AV" is I assume you meant AF as in auto focus and not aperture priority since AF makes more sense in this context.
I own a 6D and although I don't own a 5D mark II I've used it a bit and all I can say is that the auto focus of that camera doesn't seem to bee on par with the 6D's. I also own the sigma 150 2,8, albeit the OS (image stabilised) version and it has no compatibility issues with the 6D or the 5D mark II.
I've tried to find comparisons of the weather sealing performance between the two, but it seems opinion based with no clear advantage to either camera.
Comparing the specifications the 6D has
- a better auto focus system
- better low light capabilities
- WIFI and GPS in body
- is lighter and smaller
- has the latest GUI and better screen
- SD card
The 5D mark II is by now outdated and only beats the 6D with
- higher maximum shutter speed of 1/8000th of a second compared to 1/4000th of a second in the 6D
- CF card slot (although not necessary better, it can be advantageous if you own a lot of these)
- it flash syncs slightly faster
- higher resolution
I would definitely not get the 5D mark II instead of the 6D unless the price tag was significantly lower.
I think the ideal camera for each use case is different, so will try to answer them individually.
My main interest is Large Landscape panoramas and macro. As I also do Photographic Safari guiding I also do a fair amount of wildlife and Birding.
Large Landscape Panoramas
Canon 6D. You're most likely after lots of detail, very little noise, and nice wide angles, so full-frame is the way to go. The 5D has slightly higher resolution but that's about the only useful positive. The 6D has better AF, GPS, and a bit less noise. To be frank, the only difference will be how much you like either of these cameras (mostly user-interface or misc features), the image quality and general usage for landscapes will be essentially the same, but if you enjoy using it more, you'll probably take more photos with it. The only big difference I can think of is if you're shooting night-landscapes, in which case the 6D's highly sensitive central AF point will be a big help. 6D may also have better in-camera lens aberration correction (if you're not shooting RAW).
Canon 70D. You get a bit more DOF and magnification out of a crop sensor, and the 70D has the nicest Live View AF of any Canon camera to date. I'm assuming you'll be shooting on a tripod, with lots of light, and fairly small apertures. As always, there's not a huge difference, but I think the 70D would be ideal for macro. If you're not too fussed about slower Live View AF then the 60D you already have is also a good option here. Even if you're not using Live View, the 70D (or 7D) have many more AF points than the 5D Mark II or 6D, which you may find necessary for macro work (given the difficulty in focus & re-framing).
Wildlife & Birding
Canon 70D or 7D. Or your current 60D. You want the crop sensor for the extra "reach". If you get a FF camera you're going to find the animals no longer quite fill that 400mm frame, and you end up cropping to lower resolution images. The 7D and 70D have great AF sensors for wildlife, especially fast moving animals, so will be much more useful than a 5D Mark II or 6D, and a noticeable upgrade over your 60D. The 7 or 8 fps (70D or 7D respectively) are also very useful for fast moving wildlife/birds. The two FF cameras you mention are about half that.
In your position, I'd be tempted to spend the money on a crop-sensor wide angle, like the Canon 10-22mm f/3.5-4.5, Sigma 10-20mm f/3.5 or Sigma 18-35mm f/1.8 — if the wide-angle landscape shots are your motivation for going FF.
If it's all about the razor-thin DOFs, then you may well find the 50mm f/1.2 is shallow enough even on a crop sensor. Bear in mind, you're probably going to want shutter speeds of 1/8000 if you want to use that lens wide-open in daylight, which the 6D does not have.
And a warning, switching to FF can be a bit jarring when you have to "re-learn" your focal lengths, if you've been on ASP-C for a while. Those long lenses won't be as long, and the 150mm especially (as a prime) will take a bit of getting used to. But if you're finding ~250mm on your 100-400mm is plenty long enough, then it won't be a big deal.