Ye I've recently had this problem and the 7DMKII won the race. As I have a 5DMKIII and wanted a second camera for wildlife specifically as I am going traveling for 2 months across Africa with 5 game parks - Botswana, Kenya, Malawi, Namibia, South Africa, Tanzania, Uganda and Zambia. Then flying to Indonesia for another 2 seeing the orangutans and comodo dragons plus everything else along the way, so this is the reason I bought this camera.
When I can get close Il use the 5D and when not the 7D, also don't want to be swapping lenses out on safari so the 5D will probs have the wider more environmental perspective and the 7DMKII with more reach. With wildlife you can never have too much reach and even so with the larger sensor if your cropping 50%+ every time then I would say is there any need to spend that much and have a slow 7DMKII you'll be shooting 6fps at 20mp if you crop which you always do with wildlife its very hard to fill the frame unless the animals are tame. This pretty much made my decision and the fact I never print more than A2 so the 5DSR would be a bit lost for me. I also didn't want to deal with the extra size of files while traveling.
I spent 2 months traveling South america and 3 months across north america and shot 2tb of images in the 5 month stint with my 5DMKIII so with the 5DSR I would have to double it. Makes storage a bit more of a pain in the ass in the field.
Im actually so impressed with it! Its really narrowed the gap! ISO is very useable up to 4000 which is where I cap my 5DMKIII. The noise is also very natural rather than digital and the camera feels like a machine gun compared to the 5DIII 5DMKIII feel really quite slow in comparison. The Digital viewfinder is also great too.
Here are a few images I've taken recently with it. Really chuffed.
These are all crops probably 60% and this is at 640mm a 70-200mm F2.8 with a 2x ex.
Stag, Red Deer, Martindale Valley Cumbria by
Tom Scott, on Flickr
Stags, Red Deer, Martindale Valley Cumbria by
Tom Scott, on Flickr
Above are ƒ/7.1 400mm 1/320 1600ISO
Stag and his Doe's, Red Deer, Martindale Valley Cumbria by
Tom Scott, on Flickr
This one has a little crop, but if you zoom in the detail is fantastic. ƒ/8.0 400.0 mm 1/500 1250ISO
These dear are cumbrian red dear and they live in a valley almost untouched by humans. They are not used to humans and are very very skittish, and have incredible eye site and you get within 500m and they bolt doesn't matter what camo you wear the approach you take, the only thing you can do is camp out and wait and hope they don't see you and that they come close. The 7D was great to get closer to them, been struggling the the 5DMKIII and 400mm for about 2 weeks. Same techniques with the 7D got me much closer and it seems to have a lot more detail.
I would say the 5D has more latitude to crop the images look better but you get closer with the 7D… so...
Since going FF with the 5DMKIII I never thought I would go back to a crop camera but the 7DMKII really is a fantastic camera, blown away by it tbh.
Price was one of my main plusses, I bought the 100-400mm MKII with the change and a 1.4x to go with it so I have 1000mm with the 7DMKII. I had the Tarmon 150-600mm originally for my 5DMKIII but I wasn't happy with it so I decided the 7D with the 100-400 was the combo for me.
Im still waiting for the lens to arrive so will evaluate when it does.
If you need an action cam then the 7DMKII is the one. I paid £800 for mine and the 5DSr is going for about £2500. The video is also a nice feature. I agree the 5DSr is an epic camera and has all the benefits of the 7DMKII apart from price and the speed.
Obviously as above if you have a 1DX having this camera is a bit of a waste of time and your always going to use that more… but at 1/6th the price is a hell of a bang for buck you can't really go wrong with it! 85-90% of the 1DX in a small light package.
Ive also found the sensor has much better colour noise quality than my 5DMKIII. I don't find noise to be an issue with the 5DMKIII but the colour noise is a really big pain for me, not sure if anyone else gets this. But I'm forever setting the lightroom settings to 35-40 on the colour noise reduction and sometimes up to 80 on the smoothness tab!!!
If the 5DMKIV doesn't have a significant increase I will swap my 5DMKIII for the Sr but for the time being the 5DMKIII and the 7DMKII is a killer combo. I would rather have 2 than 1.
If your interested in looking at some great images taken with a 7DMKII have a look at Issacs flickr thread. His images also made my decision as they are stunning.
https://flic.kr/ps/2QwEL3