Thanks for the replies.
I have a nifty fifty for portrait and creative, and I have the 70-200 f4 L IS for sports.
Image quality required is high print quality.
I too was leaning in the direction of the 5d3 as I have been advised that IQ is everything.
I'll check out the spec of the 1d4
I was thinking of using a 2 x to give me 400mm effective but not sure if how the extender will affect IQ and apperture
What camera do you have now.?
I had a 5Diii and loved it paired with a 135L and 17-40mm for portrait and property interiors but moved on with the type of photography and needed more reach so sold the lot. Regret the 135L going a lot.
My sons started sports and I like wildlife so I got another 7D and then a 1DMKiv, I upgraded the 7D to a MKii last year. so I have used all three and still have two.
Reach is your first concern if you are already thinking of a 2x converter you might as well bin the 5Diii idea. On a f4 lens you will be at f8 so will only have centre point focus and roughly half the speed of normal focus and if you want to shoot in dark conditions forget it. Just by using a crop camera you have the effect X1.6 and on a 1Div X1.3 whilst keeping f4.
I found with football in usual UK winter conditions I needed f2.8 a lot to keep 1/1000 or 1/1250 and ISO reasonably below 1600. F2.8 lenses are not cheap but most are quality, though heavier you do get lower ISO. You also get much better isolation so if you are looking at taking pictures like the one you posted f8 will not work.
When you say high print quality do you mean large print or small for individual owners to keep? The reason I ask is if they are small (less than A3) and for individuals most will not pick up on a bit of noise I had plenty of parents wanting photos of their kids which on close inspection were not great due to backgrounds or even undone boot laces let alone a little noise.
I never really pushed the ISO on my 5Diii as always used speedlights when the light was low. But if you are short on reach a 200mm it might not be ideal unless you want to fork out some more money on a longer lens which will not be cheap.
I have found the 7Dii more than capable with high ISO it works very well to 1600 and strangely mine has a sweet spot at 12,800 which I found out taking photos of owls at dusk which is a dark as you would want to go without flash especially at a dog show.
The 1DMKiv is also very capable it is my choice of camera for taking dragonflies in flight with settings like 1/1250 f8 ISO1600 at 300mm and still being able to crop by up to 100% without noise spoiling the shot.
If I was going to a dog show to take shots like you have posted with the choice of the 3 cameras being discussed and limited to only 50mm and 70-200mm f4 I would take the 7Dii regardless of light, fps, auto focus or high ISO solely for the reach. If I had the choice of a longer lens I would take the 1Div. If it was partial dark I would first go for a f2.8 lens then either 7Dii or 1Div depending on whether it was 200mm or 300mm.
You need to be able to focus close on the subject to be able to get detail needed for quality prints, ones you have to start doing big crops you lose pixels and quality.