I have some questions question about the 5d3:
auto iso:
on my mk2 auto iso only works in AV/TV, and sets the shutter speed to 1/focal length- when shooting a wide angle lens I get motion blur and there's no way of 'speeding up the shutter' without flicking over to M or TV
with the 5d3 can you shoot auto iso in M mode (this would solve shutter speed problems and mean my aperture was fixed), and still get exposure compensation?
Exposure compensation doesn't work in manual mode but I'm not sure I understand how it could. In manual you adjust the aperture and shutter speed until you're exposed correctly according to the meter - if you want compensation then just adjust until the exposure is where you want it, or am I misunderstanding?
As for speeding up the shutter, you can select the minimum shutter speed used when Auto ISO is in use.
responsiveness:
my 5d2 takes about a second to display the image on the screen, when i'm shooting in nightclubs I want to glance down to review the image immediately after taking so I can adjust settings and take another shot before the subject has even realized i'd taken the first shot- the 5d2 is too slow for me in this, is the 5d3 quicker to display the image?
I reckon it's about half a second between the shutter firing and the image appearing on-screen.
the rate button:
I use the protect button on my 5d2 to pick the best images, but then there's no way to select only the 'rated' images, so I can scan though them quickly or even just see how many 'keepers' i've shot that session- on the 5d3 is there a way to show only rated images? I know there's a slideshow feature but basically what I want is to be able to 'rate' as I shoot, then keep checking my 'rated' folder, and when it hits 150 pics I know that i've done what i'm paid to do and can go home, at the moment I have to count up in my head the 'rated' images! also do the ratings transfer over to lightroom?
I don't think there's any way of just viewing rated images I'm afraid. The rating do transfer to Lightroom - at least that's what I've read, not tried it myself as I don't use in-camera ratings.
card slots:
I use SD exclusively, due to cost concerns and ease of use (they go straight into my laptop)- I use a CF to SD adaptor on the 5d2, with the 5d3 I know the SD slot isn't UHS compatible (not that it really matters as I doubt i'll fill the buffer), but how would performance be using an SD card in the CF card slot with the adaptor (like using the adaptor because yes SD cards are too small! and easily lost!)
if the CF card slot writes faster than the SD, then perhaps using a fast (I use 600x) SD cards in the CF card slot is a great alternative to expensive CF cards!
For this to work, you'd need an adapter which supports both UHS for the inserted SD card and then UDMA for it's CF connection to the camera. I'm not such adapters even exist but, if they do, they're going to be rather expensive.