For me, it is easier to get the appropriate angle when shaving or stropping with the 6/8. It makes no difference getting into tight places, like under the nose. YMMV. Obviously, the wider blade holds more whiskers & lather before having to be wiped (on a Chimensch sponge) or rinsed (and possibly dinged) under a faucet. There isn't a great deal of difference, and I would buy a 5/8 razor I liked, but given the choice, I prefer the 6/8.
I agree on this point for sure. One of my all time favorite razors was a 5/8 Thiers Issard Super "Gnome" however 6/8 is what I have gotten used to as a daily driver and it is what I would seek out when purchasing another razor in the future.