Removing/installing the rear wheel is a PITA, I can do it pretty quickly but hate every minute of it. No problems installing the tires on the rims.
You can find data all over the place on the safety of fatter tires on thinner rims. It was common place in the early days of MTBing (when I started).
The CCX has an inner rim width of 19mm.
On sheldon browns site(go down to the table with red and green and also look at the note under the table):
https://www.sheldonbrown.com/tire-sizing.html
Many people exceed this by quite a bit and dont seem to have problems. Probably not a good idea if you go tubeless but then again, many people do it without issue.
I also found this document from DT Swiss:
https://dycteyr72g97f.cloudfront.net/uploads/W0X1900AEIXS012610/MAN_WXD10000000866S_WEB_ZZ_001.pdf
The tire profile definately isnt ideal (being more pointy in the center) but I didnt notice anything drastic.
IMHO, the 50mm tire front and rear would probably be better for most people than what Im using. That being said, the 55mm front is definitely more comfy
Did a 36 mile ride tonight (about 25%gravel/smooth hardpack and 75% asphalt/concrete). Im pretty happy with the setup now. Running 35psi in the front and 40psi in the rear and that feels about perfect. Even did some of the harsher stuff with the forked locked out and it was comfortable enough for me to consider going to a rigid front fork in the future. If I do that I will probably go with a thru axle setup in the front which will require a new wheel so I would go to a wider rim at the same time.
The conti racekings were AWESOME tires, I liked them alot. Supposedly good rolling resistance and excellent gravel traction. I was getting pretty quick wear on the rear im guessing to the power the CCX was putting down (the center knobs had a very noticable feathering wear pattern which is what you would get if your putting alot of power down). Im guessing they would have gone bald at 1k miles.
As a comparison, the 27.5x2.8 nobby nics on my bulls evo 3 27.5+ (which by no means are a good onroad tire) at about 2.5k miles still had about 1/2 tread in the rear.
This tire also looks interesting, might try it in a few months in the rear with the 2.2 conti raceking in the front
I love tinkering and trying all sorts of stuff.