Hmm. There are no really hard and fast standards for roll film formats larger than nominal 6x6 (usually 56 x 56 mm). Nominal 6x7 is usually 56 x 68. Usually. Nominal
6x9 (same as nominal 2.25" x 3.25") ranges from
56 x 78 (late Graflex 2x3 roll holders with pin rollers) to as much as
56 x 84 (for example, Linhof 6x9 Super Rollex and
Mamiya Press).
6x8, as realized by the Fuji
GX680 is
56 x 75.
As has been mentioned above, the GX680 is an SLR and Mamiya Press (includes Super 23 and Universal) cameras are rangefinders. What hasn't been mentioned explicitly is that the GX680's cataloged weight is over 4 kg. The Super 23 weighs roughly 4 pounds. Jeff, which would you rather carry?
Previous posters have suggested various press cameras. In spite of their name, cameras in the Mamiya press system are not typical press cameras. The typical press camera folds, has at least a double extension (> 200 mm) bellows, accepts lenses in shutters on boards and may have a range finder. Some, e.g., Linhof and Horseman may have range finders that can be cammed to nearly any lens. Kalart rangefinders as used on some press cameras can be adjusted for a range of lenses but the calibration process is so time-consuming that in practice the RF is good for only one lens. Hugo Meyer RFs as used on some press cameras can be adjusted for only one lens, typically the standard issue normal lens.
Little field cameras have more movements than press cameras, rarely have coupled rangefinders. Most, not all, fold.
Most press cameras have some movements. Practically speaking Mamiya Press cameras have no movements. Movements can't be used when shooting hand-held.
When I moved up in format from 35 mm still to 2x3 I was strongly tempted by the Mamiya Press system but ended up with a 2x3 Speed Graphic and, later and additionally, a Century Graphic. Regardless of what enthusiasts say, these wee beasties' only useful movement is 19 mm of front rise. Linhof and Horseman press cameras have more. I don't regret getting my little Graphics, which I shoot nearly exclusively from tripod for scenics and closeup (mainly flowers).
No one has mentioned 2x3 view cameras yet. I have a couple of 2x3 Cambo SCs, like them very much. They're less portable than 2x3 press cameras and somewhat slower working but more flexible. Same goes for other 2x3 view cameras. My lens diary (see
http://www.galerie-photo.com/telechargement/dan-fromm-6x9-lenses-v2-2011-03-29.pdf and I've added a few lenses since 2011) describes the lenses I've used on my Graphics. All but the 60/14 Perigraphe can be used on my Cambos and I'm working on making the Perigraphe usable too. My 900/10 Apo-Saphir can't be used on my Graphics, can be used on a 2x3 Cambo.
Jeff, given that you're inclined to work from tripod I think your best options are the GX680 or a 2x3 view camera with a Horseman or Super Rollex roll holder. Press and field cameras on tripod are nearly as slow-working as a view camera and are much less flexible. If you choose a view camera, don't worry much about lenses. The world's awash in good quality lenses of all focal lengths that cover 2x3 and larger formats.
Good luck, have fun and remember that whatever you do will be wrong,
Dan