[j.blay]

You listed the same source I use. I put an 18:1 Cosmo Black set on my FG800. Fit was perfect. Also bought their matching strap buttons.
Last pic shows the 21:1 510's with the hap and locking functions on my Jake Robinson Brazilian. Minor advantage in being able to adjust for more string break angle at the nut on the headstock. I obsessed with getting the best of everything on my Jake Robinson. I personally wouldn't spend the extra on my Yamaha, but you have a much nicer model than I have.