The Peak Design is an excellent sling - I use it on my 645Z, attached via both tripod plates.
My black K-1 travels with a Black Rapid, which is part of a double harness for when I shoot events with two bodies. I could never get the PD Sling to sit really comfortably with the K-1, but I still use PD clip to connect a short back-up tether in case the BR sling unscrews itself from the tripod socket. It hasn't happened to me, but I have heard horror stories....
My silver K-1 still hangs on the
ONA Presidio strap it was supplied with. It's a very elegant black canvas and brown leather affair, and is plenty long enough to be used as a shoulder sling. Just looking at the C.R. Kennedy website though, what few stacks now remain are supplied with the standard O-ST162 strap