Statistics. If you love the image quality of your Kodak-equipped 'blad and shoot portraits, my experience of all opinions I've taken part of is that you're going to prefer that over the CMOS.
The most accepting photographers concerning the CMOS seems to be landscape photographers, but they're more into long exposure, high ISO and high dynamic range than subtle details in the skin tone and skin texture. Some even use Lightroom instead of Phocus and Capture One, just crazy
The only thing I know for sure is that they render differently, colors will not be
exactly the same. I don't think the older system will win in any objective measurable aspect, but you might just prefer the look of the older system.
Honestly I think there's some psychological aspect in it too, CMOS has a bad reputation from back in the days when it was not very good, and in later years that MF has been CCD based has become some sort of differentiator, use this more "film-like CCD" in MF rather than the "artificial looking CMOS" in 135. I know this from the HiFi audio work I've done, you hear what you want to hear and I think it's just the same that you see what you want to see. In the very rare blind testing I've seen of web-sized photos with skilled post-processing people just don't seem to be able to differ. That results are different everyone can see, because it's very hard to make two different cameras to look exactly the same, but which one is better...? But evenso, when the photographer works with one file or another he/she may feel that there's more or less struggle to get to a look that is preferred. So regardless if the "superiority" is real or imagined the look has relevance.
Another interesting observation I've made that Leaf and Phase One owners tend to think the Kodak tech is not very capable and MF got just so much better with Dalsa, while the Kodak is working excellently in the Hasselblad camp. The Dalsa is a little better in those classic measurable aspects like DR and tonality, but the truth is that the Kodak is more than adequate in these aspects for most types of photography and then it just comes down to which look you prefer.
I have raw test files both from H3DII-50 and CFV-50 (should be very similar to H4D-50) and H5D-50c, but not shot side by side on the same subject unfortunately. What is really needed here to help Richard is raw files of side by side shots of the type of subjects he's interested in, which he can download and process with his workflow. Anything less than that will just be some other photographer's opinion. Unfortunately it's hard to come by on the net, but we'll see in this thread. Otherwise a Hasselblad dealer should be able to provide this.
If I was working with portraits I would be very careful not to mess with my workflow and look if I was currently very pleased with the results. So just upgrading because it's newer is probably not a good idea, you really need to check out how it renders.