The 5xc is like a 5xb with a room addition on the bottom with its own entrance.
I have one but I use it for my DSLR crop camera, a Canon Xsi. I put the Xsi wearing a Tamron 17-50/2.8 in the top and have a Canon 70-200/4 riding in the bottom with batteries and cards riding in the pockets.
I bought it specifically for this DSLR kit as the lenses, even with the "smaller" primes, are just flat-out big.
I don't think I'd use it for an RF kit though. Too big for my taste for RF, though lots and lots of people use F-803's, which are even a little bigger. (Right now, my F-803 is holding my 4x5 Graphic).
I like the bag because the top-end is like the F-5xb which is my ideal all-round photo bag.