I'm going to buy me one, eventually. Right now I'm busy still with ultralight/superlight replacement of all my backpacking/trekking gear. Everything's so expensive! And I have a GA645 I'm still breaking in. I love the optics, which is the same lens design as yours by the way, except for one thing. I don't like the bokeh on these lenses fully open. I think it has to be stopped down to f8 before it starts looking real interesting to me and my taste. Other than that, the optics are razor sharp and very nice gradation. I think it's the coating.. It's just simply superb.
Did you buy yours for 6x6 or 6x7 primarily?
I think I would wind up shooting 6x7 but honestly if you're talking about 8x10 paper or 16x20.. 6x7 negative is an oddball format.