I guess form I am curious about the reputation that the Zeiss lens have for sharpness and resolution. I have NO experience with Zeiss lenses and only know what I have heard. My Mamiya lenses may be just as sharp and have equal resolution????
The word "superb" is very often used when Zeiss lenses are mentioned.
And though they are not all the same, and some are more superb than others, they indeed are superb.
I by no means know all Mamiya RB/RZ lenses, but the ones i do know are that - superb - too.
And i have no doubt that, with the same "they are not all the same" proviso, the ones i do not know indeed are superb as well.
Some people say that they can tell the difference between images produced by Zeiss and Mamiya RB/RZ glass. And perhaps these 'lens families' each indeed have a unique signature.
But i can't.
My take on this has always been that the lenses of each are more than good enough. Not something to base a decision between the systems on.
So i made my choice based on other considerations.
And i would say that if you are comfortable with the RB, there is no reason to change (except perhaps out of curiosity, to see for yourself).
But that's just my look at things, of course.
David's question is a good one: do you need to sell the RB to try a Hasselblad?
If so, don't.
If not, hang on to your RB and just give the Zeiss thingies a try.