I have seen the result of an uncontained failure of a CF6 on an A300 600 where compressor blades from the failed engine embedded themselves in the other one....
Seems like there was still enough energy for that after all.
..............
Really?, the most I've known of on the A300 is a few bits sticking into soft nacelle skin but never making it through to the actual engine insides.
.......
Four engines are almost always better than two.
Agree, you have 3 times the chance for nailing any two engines in an uncontained failure on a quad if that's what you mean by better.