A couple of things. I agree that a Hassy is a better camera, but I don't think that it is enough better to justify the additional cost of ownership. I have a Mamiya 645 and love it. The film is big enough to make very nice 16X20 prints, but I would certainly agree that the additional negative size of a 6X7 would be great. I also use a TLR to get my fix of 6X6 negatives.

I think that you should look at the way you intend to use it, I think that the Mamiya 645 Super or Pro work great for hand holding with the winder grip. The RB and RZ are awesome for tripod based work thanks to their rotating backs. I don't know the Bronica models as well, but they have a good reputation and are also available for a very low price right now.

Have fun!

Paul.