Well in 6x7 format you'd be lugging a lot of slow glass to get to that field of view. And furthermore, the top shutter speed on your rb is 1/400. So... the lens isn't fast and with that slowish top shutter speed, you're pretty tightly constrained. Finally, if you consider that we're talking about tele subjects here, the enlargement factor is not that different, comparing 645 and 6x7. By that I mean: if we were talking about a wider field of view, then I'd definitely argue that 6x7 is clearly superior. But for a narrower field of view and tele shooting in general, I just don't see much advantage in 6x7. Combining all these things, I do not think that you will see much format gain by shooting 360/6.3... as opposed to shooting 200mm in 645 format.
N.b. the [excellent] manual focus mamiya 200/2.8 apo lens (which I have and love) sometimes goes for $500 or so, and it's fast enough that I can shoot it at 1/1000 sec or faster routinely without going to ISO 400 film. It kicks the 360/6.3 all over the place. The 350 KL would have a better chance against it, probably.
For wider fields of view, I tend to go to larger formats; for tighter crops and tele subjects (sports, wildlife etc) I go to smaller formats like 645 and 35mm.
Mind you, for static tele, the 360 is peachy.