Treeman - you have finally started to whittle the list down for yourself
I too use to shoot a Mamiya, not the RB but the faster and easier RZ, but I always envied the old dedicated portrait lens for the RB - was it 127mm or 140mm with the 3 discs for diffusion that dropped in the back. Now that I have gone away from medium format altogether and rely purely on 35mm digital I have replicated that Mamiya portrait lens with the Nikkor 105 f2 DC lens - it is an absolute cracker for portraits.
Those who have not used a DC lens (DC stands for Defocus Control) won't understand the difference it gives over a normal prime used wide open. You can do that too, of course, by leaving the DC alone and just using the lens at f2. The result from the slightly longer lens is very close to the 85mm with the slightly faster aperture (either of them).
There is another advantage too, you can get a mint, used 105DC very reasonably in comparison to the 85mm, even the f1.8. They are about the same price. The DC lens can be used to give wonderfully dreamy backgrounds and a razor sharp eye, or you can use it to diffuse the highlights that work in such a way as to reduce skin blemishes naturally, in camera. It takes a fair bit of experimentation to understand it, and the focus changes when you use DC - set the DC BEFORE you focus and then the focus is where you put it, of course. Otherwise it can rear focus on you.
Brilliant, old fashioned build quality. A slip out lens hood, but a very well protected front element anyway, it is tucked away in the depths already, I see no reason to fit a UV filter, you would have to start poking a stick down the front of the barrel to get to the front element. The AF is old, slow and noisy in comparison to AFS lenses, but you would use this in manual anyway unless your eyes are dodgy, the viewfinder snaps into focus beautifully and you can see the effect of the DC if you use the preview button.
Give it some thought - but I would go for the 105, not the 135. The longer lens loses something that is hard to define. I had them both from Nikon Pro to try before buying mine. I don't do pictures on line, I don't have a website, or flickr or facebook or any of that crap - I don't know how to work them anyway and I am not really disposed to spending time to find out....I would rather be outside.
However, there are PLENTY of examples from other photographers out there for you to see just how this lens performs.
There are two kinds of photographer; those who have never used a DC lens and know it is crap, or those who have used one and think it is great.