After posting on one of the forums about this a while ago I finally got around to posting some of the results of the test for people interested.
Complete results of the test (with RAW files) can be found at http://niels.com/tests/phase-vs-hasselblad.html
A short summary:
We did a test setup where we put a Phase One P65+ and a Hasselblad 50MS side by side. Various medium format photographers were invited and their observations are noted below.
Phase One P65+ on Phase One (Mamiya 645) body with Mamiya 80mm f/2.8 lens (Dalsa 60MP sensor)
Hasselblad H3DII-50MS with Hasselblad 80mm f/2.8 lens (Kodak 50MP sensor used in single and multishot mode)
Setup: (see attachment total.jpg)
Shots were taken at 1/125s - f/22. Phase One photos were processed with Capture One Pro 5.0.1, Hasselblad photos with Phocus 2.0.
Gray balance was applied to the neutral gray on the test chart in the photo, all other settings (sharpen, saturation, etc) were on zero or switched off in both programs.
Observations while shooting were that the viewfinder of the Phase One camera shows a very small picture compared to the Hasselblad H3DII, it feels like looking through a 35mm camera and it is difficult to focus. Also, autofocus on the Phase is slower and can't be intervened.
Flash sync on the Mamiya does not go up from 1/125s where Hasselblad goes to 1/800s. However Phase One has promised this will change.
The display on the Phase One back is tiny. As far as design goes, most people liked the Hasselblad better, although the MS is heavier because of the Multishot mechanism.
Observing the images there were quite a lot of differences:
Sharpness: The Hasselblad lens is a little sharper than the Mamiya, but the difference is not that big. There is however a huge difference from the Single Shot to the Multishot file, almost as big as when comparing 35mm to medium format.
Noise: The Dalsa (Phase) sensor produces quite a lot of noise compared to the Kodak (Hasselblad), especially in dark colors.
Dynamic range: Especially in the highlights the Phase loses detail before the HB does, even in single shot mode. Again, multishot makes a big difference.
Color: The Kodak sensor produces more saturated colors, although the difference is not so big. Color interpretation is quite different.
Tones: Gradients on the HB are much more subtle, Phase makes 'jumps' on gradients where HB tonality is more continuous.
Sensitivity: The Phase was about a third stop lighter than the Hasselblad, both at ISO 50 and f/22.
High ISO: Phase's ISO+ makes a huge improvement at ISO 800, where it leaves HB in the dust. Higher ISO speeds are such bad quality that they are basically obsolete. At speeds of ISO 50-200 Phase is noisier, at ISO 400 they are just about the same.
Our main conclusion was that the optical difference is not the bottleneck of the performance in medium format (as it is in 35mm), it is still the sensor. Not the number of pixels, but the way they are interpreted. The Multishot files show a degree of color accuracy and sharpness that a single shot sensor (any single shot sensor) does not even get close to. Too bad for those of us who like to shoot subjects that move...