Wow Alan! You've owned all three of the Pentax 645s. Impressive! And what a way to get the Nii!!!
I've been drooling for the 35mm and seen it in the store a couple times but never had the money for it. I really love my Mamiya 645 series 35mm lens and would love to have one for my Pentax as well.
As for ultimate sharpness in medium format I have no doubt the Mamiya 7 is good, but I suspect that Fuji GF670 might be even sharper. It continually amazes me!