"The other question is reliability. I would imagine the Hasselblad system would stand up to use better than the Mamiya 645. How about the electronics in the newer 645 models? And problems?"
If new, the Hasselblad would be on top. However, used, it may have more than its share of wear and tear. Of course, the same may be said of other cameras, however, more likely to have been in amateur use and have better care.
If both were equal, it seems the Hasselblad would make more sense and is what your preference is anyway.