I got both the GA645i & GA645Zi cameras.
The diff between the GA645i & GA645 is there is an extra horizontal trigger button when u shoot the portrait position. "i" also represent that the camera will self detect the ISO rating of any fuji film that you load into the camera. Note, only works for Fuji films.
This camera comes in five variations, four of which are essentially similar.
GA645 has a 60mm f/4 lens
GA645W is the same as above but has a 45mm f/4 lens
GA645i is similar to the GA645, except that it also has a second shutter release and barcode reader for Fuji medium-format films (it automatically sets the film speed)
GA645Wi is the same as above, but with the 45mm lens.
GA645Zi has a 55-90mm zoom lens and is dolled up to look like a Contax G.
For the GA645Zi, it's a versatile zoom in medium format. But the focussing can be slow and need some getting used to as they may not focus on the area that you desire, so do look at the distance scale in the EVF to check. Some extracts from the fuji site:
http://www.fujifilm.com/home/press/pr_ga645zi.htm
I don't work for Fuji!!!
Main Features of the Fujifilm GA645 Zi Professional 1.6x High Performance Zoom Lens The F4.5/55mm to F6.9/90mm zoom lens of the Fujifilm GA645 Zi Professional corresponds to a 34-to-56mm zoom in the 35mm format. Zoom action is quick and easy thanks to a smooth zoom lever. The zoom viewfinder linked to lens zoom action always shows actual picture area and has automatic parallax compensation. Super EBC Fujinon Zoom Lens Fujifilm's original Super-EBC (Electron Beam Coating) dramatically reduces unwanted reflections and glare. Superior sharpness extends into the far image corners, while even light distribution delivers brilliant, true-to-life colors for an overall picture quality of truly professional standards. Hybrid Autofocus The GA645 Zi is equipped with both infrared active and passive systems and automatically selects the most suitable method for the prevailing lighting condition. It responds swiftly to moving objects for quick, successive shooting. Users can switch to Manual Focus for unlimited control of focus settings. The Next Evolution in the Fujifilm Barcode System The GA645 Zi Professional incorporates an advanced version of Fujifilm's breakthrough Barcode System. Features include: キ Automatic Pressure Plate Change for 120/220 Films -- The film barcode scanner in the GA645 Zi Professional automatically distinguishes 120 and 220 roll film, and switches the pressure plate for optimum flatness. Manual switchover is available for film without the barcode logo.
キ Automatic Film Speed Setting -- The Barcode scanner reads film speed and adjusts camera settings automatically. Manual override is possible as well.
キ Automatic Film Advance -- Film is wound forward to the first frame automatically. There's no need to watch for the frame marking; a buzzer sounds when the film is at the last frame.
The Fujifilm GA645 Zi also features a new Slow Synchro AE mode that permits flash synchro with slow shutter speeds, so there's no shutter speed limitation when using the built-in flash. The camera also features a large, backlit LCD so professionals can see vital information at a glance, even in the dark. A lens cap sensor warns when the lens cap is still on, and the viewfinder has a built-in eyesight compensation. In addition, Fujifilm's GA645 Zi Professional comes in a sophisticated titanium body that is lightweight, strong and highly resistant to shock and corrosion.
See the below url for more info. Hope it helps.
http://www.dantestella.com/technical/ga645.html
BTW, if u have not known, the Fujinon EBC lens used in the GA 645 series cameras are the same lens systems that are used in the Hasselblad H1 & Xpan camera lenses. So, for Hasselblad to be willing to use a Japanese lens in place of the usual Carl Zeiss or German lens, u can expect very high quality image from the EBC lenses.