The later lever wind Graflex backs are much nicer than the knob wind ones. Also, film flatness is better in the Graflex backs if they have the needle rollers either side of the film gate: these are almost never present on the knob wind types (some may have been retro-fitted) and usually are present on the lever types.
The Horseman backs (Arca-Swiss ones are identical, Wistas not identical but very similar) are much nicer to use and do feel better made. You are right that the Graflex backs are a bit lighter though.
Also, be aware that the Graflex '6x9' back is actually closer to the 6x8 format in size. My Graflex '6x9' back makes 57x78mm images, while my Horsemans are the more or less standard 56x82mm. You may prefer that, or not, but it does essentially mean that you are getting 6x8 sized negatives but using film at the same rate as you would for 6x9: you don't get the extra shot per roll that true (Fuji) 6x8 gets.
Peter