First let me say that there is no advantage in having a "Crop Factor". It is one of those phrases that is thrown around as if you magically get more reach. In reality it is a smaller sensor that wastes or throws away the outside edges of a Full Frame sensor. It just crops your full frame picture down to a smaller size.
However, there is an advantage in having a sensor with a denser pixel count. While I wouldn't have agreed with this back in the 7D days, I would have to say now there is an advantage of having the 7D II body and its increased resolution.
On Jan 1st I was bored and I had a test I wanted to perform to confirm some of the things I was seeing with the 7D II. I set up a test with the 500mm, shooting in manual live view focus mode, shooting at F/4 I took a make shift ISO 12233 chart I had printed off line. I started at 15 feet and took a base shot with the 5D II. Then at 18" intervals I took shots to give comparisons at x1.1, x1.2...etc. I did this with the 1D IV and the 7D II. Then I cropped the center of the pic and resized all samples to the exact same size. My thought process is that this is what we would have done with a real life pic. We would have cropped to get the exact picture we wanted. The end picture would have been either printed or displayed in the exact same size.
What I found is that the 7D II x1.2 was just a hair better than the 5D II x1.0. At the 7D II x 1.3 the 5D II x1.0 clearly beats the 7D II x1.3x. So what I find is that the x1.2 + just a little bit is probably the benefit we see in a crop body where resolution counts.
With the 1D IV the 5D II the 5D x1.0 is much better than the 1D IV x1.1. There is minimal if no additional resolution value using the 1D IV.
The 7D II held an x1.2 advantage both over the 1D IV and 5D II.
Here is an example in real life. The Blue Jay is the same area and about the same distance as the Female Cardinal. The Blue Jay is with the 1D IV and the Cardinal with the 7D II. Shot at 500mm same time of day. Close to the same settings. You can pick the shots apart and say maybe this or that was done wrong, but I am seeing similar shots over and over again.
Notice the Blue Jays eyes compared to the Cardinals. The Cardinals have just a bit better resolution.
BB1H5832 by hdnitehawk01, on Flickr
CQ2A2128 by hdnitehawk01, on Flickr
Now the negative of using the 7D II.
The 7D II is not as precise as the 1D IV. The 1D IV seldom misses. Usually if it misses it is because of me putting it in a bad condition.
The 7D II is random. It will have the bird in focus within the DOF but it will miss the critical point that puts the eye in sharp focus. The 7D II takes a +4 to +6 with the new 500mm. I am thinking about shipping it to Canon to check the AF system. I cannot trust it for a critical shot.
The 7D II is slower than the 1D IV. It also seems like it hunts for focus more.
I haven't given up on the 7D II yet. I have seen the benefit of its increased resolution on small critters and birds in focal length limited conditions. But its AF system has to perform better.