There's no getting away from the fact that, on the current 80MP backs, retro-focus designed lenses perform better wrt shifting. That's just the way it is.
In terms of the other variables - sharpness, color rendition, bokeh, flare, weight, cost etc. - it's less clear cut.
There's little between them in terms of resolution/sharpness. In the real-world images I've seen I'd give it to the R/S, but only just, and in all real-world applications, with appropriate sharpening, the difference is negligible. (In terms of the MTF charts, the R/S looks superior - but the horizontal scale R/S use is to 45mm, whereas the S/K scale is to 100mm, so the differences naturally look dramatic). As far as color and bokeh are concerned: the R/S renders punchier color, the S/K is more restrained. I prefer the S/K. In terms of Bokeh - no question - the symmetrical design of the S/K is superior and leads to nicer rendering of out of focus highlights. Flare? Retrofocus designs are more susceptible. Weight? The S/Ks are lighter. Cost? The S/Ks are more economical due to their design (fewer glass elements - however, if cost is measured per lens element, this makes them considerably more expensive than the R/Ss).
Someone once described the differences as akin to the differences between a high-end digital audio setup (R/S), and a high-end analogue audio setup (S/K). In terms of a practical approach to differentiating between them, I think that's about right.
Jim
P.S. As an aside: We'll never see a new consumer-grade MF CCD DB again. Even R/S's current W/As have been shown wanting with the largish CMOS sensor in the IQ250, so I get a feeling that for a new generation of even larger ('full-frame') CMOS sensors, we'll see a new range of even more expensive retro-focus W/A lenses from R/S.
ken