Thanks to Ryan from Reef, Chris from Nauticam, and Chris from Phase I got to play with the Phase 645 in the pool a month or so ago. The detail is pretty impressive. This example was shot with the 28mm Mamiya. Ideally I think this camera is best suited for underwater portrait work say with a 50mm, as the high res benefits are going to be most evident with a portrait setup rather than moderate wideangle.
First is a slightly cropped image in the horizontal plane, and the second is 100% crop. (A little over sharpened for the magnification, and a skin softening filter run to soften the makeup and pores) - pretty impressive detail

