I have looked into this extensively since I am putting on the 5 degree RCI sliders. It seems the main bar you would slide on is basically in the same place and the degrees go up from there. I would think as above if you were a serious rock crawler you may want the 20 degree to add that extra clearance as the slider goes away from the vehicle. Some have said and showed pictures and from their experience they believe the 5 degree may keep you a bit more away from an obstacle. Others have said that RCI says there is only a quarter of and inch difference with the size of the step between the two. However, they have also said the 5 degree works better as a step. Many have said the 20 degree is fine for them as a step and some think it is just OK.
It seems it comes down to look and preference. I bought them for a step and in case I happen to slam on them. I am not planning on sliding on them just for fun. There is plenty of rock crawling to do without ever touching them or just slightly knocking them at times. If, however I come down on a rock or a tree stump I want to be sure my rails will protect me.
There are lots of opinions out there and I believe I had made the right choice for me. I am also hoping the 5 degree keeps more rocks off the doors. Either one I am sure will be great.
23 Bronco Raptor, code orange belts, keyless, lux, leather trim/suede seats, carbon fibre, shadow black