I've had a Bronica GS-1 for several years now, and I really like it. I don't shoot 645, so I don't really have anything to compare it to. One of the first things I did was remove the speed grip and swap the bulky prism for a WLF. Shooting at waist level, this is a great camera hand-held. Nonetheless, I do do most of my shooting with a tripod. The GS-1 is not meant for portrait orientation, but for me that is not a problem. For me, the biggest drawback of 6x7 is negative storage. One roll of 120 will not fit on a single page; pretty minor, I admit, but it is irksome.
One other thing... the shutter kicks like a shotgun (and is nearly as loud... don't use it at political rallies) so you'll want to use the mirror lock-up - but not shooting hand-held. Someone, er... told me about that. Wasn't me. Never happened.