I absolutely love the Hasselblad's and that is what I want, pity they don't seem to do the long exposures so well.
Have you looked at the H4D-40? Same latest-generation sensor as the Pentax 645D (but again, as with the H3DII-31, it all depends on how well Hasselblad implemented it...)
Hasselblad do permit the H4D-40 to shoot 4x longer (240 sec), which is encouraging.
Ray