The reason I took the Canon route is that I didn't want to modify the lenses' mount (the Nikon case with Leitax adapters), as I also shoot with film R bodies. As for the 1.6X cropping, the FF bodies like the 5D wouldn't accept all my R lenses, especially my trusted 28-90 ASPH.
I use adapters of the German brand Quenox ordered from enjoyyourcamera.com. They are of good built quality, not very expensive, and the R-to-Canon also features focus confirmation.
Shooting with the R 60mm f2.8 Macro has given many acceptable pictures. I shoot in aperture priority or manual mode. I focus with no problems with apertures up to f5.6; after that, there is no focus confirmation response. So, the best solution is to focus wide open, then select aperture through the on-lens ring, and finally compose and shoot.
The pleasant surprise was that all the metering modes appear to work fine, and so does exposure lock; I didn't try machine-gun shooting.
For accurate focusing, I use the live view alternative. Live view works fine, with 5X and 10X zoom, but it drains the battery, as expected. (Otherwise, the battery life is quite long.) I even tried hand-held live view with the 80-200 f4 on! The few keepers were with nice colors and clarity, though. All in all, the combination is a good poor man's alternative to M240.
Now, the 40D with Hasselblad lenses is a different story. No focus confirmation and the heavy lenses make live view and shooting on a tripod a necessity. Aperture priority or manual again, no limit to f5.6 for focusing, since there is no confirmation available, and the lens must be stopped down via both the on-lens ring AND the depth-of-field lock button. There is no need to worry about how to set the speed on he lens--it will be set via the Canon on-body function. There is no communication of any sort between the lens and the camera.
Perhaps all these are known to most people here. When I started reading various forums about medium format lenses on Canon (or Nikon) bodies, most posts were negative--especially as regards the quality of the images. Some went that far to talk about a degradation in IQ because the MF lenses, they claimed, were considered of low quality for the demanding 36X24mm sensors of today. Well, so far I saw no such falling in quality, and I have only used the 80mm Planar; I look forward to shooting with the 180mm Sonnar. Again, then, Hasselblad lenses on Canon bodies is also worth trying.