I have the GW690II with the 90/3.5. I think that the III may have a better finder, but I've only looked through one briefly 18 months or so ago, and the impression didn't last, so it may not be that much of an improvement. I have a 40mm hotshoe finder made by Cosina Voigtlander for 35mm cameras, and it gives a much better feel for what the camera's seeing than the small, cramped finders on the 690 bodies. It's very close to the correct framing for the 690 with a 90mm.
I'd seen lots of Hassy and Mamiya RB shots from studio work before getting my 690III, and both B&W negs and transparencies from the 690II surprised me with their sharpness and contrast. It looked very close to 35mm resolution standards transferred to MF.
Lee