"Not to be a jerk, but Mamiya had/has an 80mm F1.9 lens:"
...and I am well aware of this. I have two of them. That lens is the whole reason I bought my Mamiya 645 equipment, and the whole reason that I would never even consider any other 645 system for more than a brief moment. It is the reason I went for a 645 instead of an RZ. The fastest lens possible is extremely important for a good deal of what I shoot.
What I said is: "f/2.8 is as fast as you will be able to get with a similar angle of view", meaning a similar angle of view as a 35mm lens in small format, which is what the OP wants. For 6x7, the OP needs a 65mm to get a similar horizontal AOV as the 35 on small format, or a 75mm for a similar vertical AOV. For 645, the OP would need a 55mm lens, not an 80mm.
Besides, the question is in regards to 6cm or longer frame spacings, so I limited my trivial comments (mention of the Pentax 105mm 2.4 and 90mm 2.8) to these systems.