Hi folks.
...I can't decide between the 7D mk2 or the 1D mk4, ...
Just looking for some input.
Thanks.
Steve.B

:t:
Hi, I have both a 1D Mark IV and a more recently purchased 7D Mark II. Both were s/h purchases. The 7D Mark II is surprisingly heavy compared to my 5D Mark II which has the larger prism.
As John has said, both are very good cameras, and in general, they deliver. My 7D (original) for no obvious reason sometimes didn't - even on what I thought was an easy thing to focus on. The 7D Mark II has some nice modern features, but my gut feeling is that I'd choose the 1D Mark IV for the more demanding and important shoot. I've used the 1D Mark IV extensively with an EF 500 F/4L IS, and to a degree with an EF 300 F/2.8L IS. I've also used them with Canon extenders (both 1.4x Mk I and 2x Mk II & III), and here my hit rate of really sharp shots dropped somewhat. Is it me, AF-MA settings or what?
The buffer on the 1D Mark IV held up when I needed it when shooting the Tour of Britain peleton - something over 100 shots in one long burst as the cyclists rode past my position in 2014.
Unless I've missed something (and I probably have), the method of choosing the AF pattern on the 7D II can take some time getting back to the one you've just left! Both bodies offer a video facility, but I use a "proper" camcorder for video. Not sure whether it's quite so important now with pros using high resolution standard sized bodies, but the large body of the 1D Mark IV signals that you're serious, and in my case, has helped me to retain a good vantage point when covering a local newsworthy event. OTOH the 7D Mark II with the EFs 15-85 makes a capable, but heavy, outfit for a day out doing things other than photography.
I've never had any problems driving Canon's Big Whites using a 1D Mark III or Mark IV, whereas I did have problems some years ago using a 5D when shooting birds. The camera simply stopped when shooting with an EF 300 F2.8L - changing the lens to a small zoom, and it was fine. So far, no problems with either of my 7D models - perhaps the later batteries have a better performance.
The AF on my 1D IV was fast enough to re-acquire a kingfisher after it flew off a perch to its nest hole - more or less directly away from my camera position. In a sequence of 4 or 5 shots the first shot after leaving the perch is very soft, and subsequent shots get sharper, and the last pair are more than acceptable.
Buy either and enjoy!