Matt, the reason I don't have a wide angle lens in my group is because I have an SWC, and also a 50mm for the Mamiya 6, and a 45mm for the RF645. So I've certainly got the wide angle lenses covered. The main thing I'm looking for with either system is telephoto lenses.
GWC, I do already have the 6x4.5 format in the Bronica rangefinder, but I only have two lenses, a 65 and a 45. I feel there's no too many options there besides use as a hand-held or hiking camera, which it is great for! 6x7 is not a format for me. I've tried it in the past and don't particularly care for it.
Mark, I agree with you. I love the 6x6 format. Square is great, and I think I'm leaning more towards the blad because I can get 6x6 and 6x4.5 all in one camera, whereas if I went the Mamiya route, to go square I would lose a lot of negative.
I'm still thinking. But, like I said, I'm really leaning towards the Hasselblad simply because I already have backs and because of being able to shoot square and 6x4.5 at the same time, and not having to turn the camera on a tripod (sounds simply, but is really annoying after a while).
Thanks everyone for the suggestions so far!