Santa Claus and the UW camera

Everything you mention will do the job well, if you use it well.

Any other criteria? Size, weight, cost, anything to help differentiate the alternatives?

The Olympus with the 60mm macro lens is awesome, for example, but may not meet other criteria.

Yep, other criteria will be decisive.

For example, I am strongly biased in favour of my system (Olympus EM5, 60 mm macro lens, Inon S2000 strobes, Nauticam) because it takes great macro photos but also because it is small, light, and affordable. I get 1:1 macro with excellent working distance and everything including camera and housing and port and arms and flotation and focus light and batteries and chargers fits in an ordinary photo backpack. However it is definitely not the last word in IQ or DOF. I could certainly get technically better shots with a FX system, but for me the marginal benefit would be far outweighed by the marginal cost (financial as well as practical).

Here are two example from last weekend. These are pretty much SOOC with only minor crop and contrast adjustments and yeah the composition is crap, but this is about as good as I can make with this system. Only you can decide if this is the kind of photo you want to make and the IQ you are happy with.

I forgot to answer your question. If anyone asks, I'll tell them to hold out until early next year for the E-M1 mk II, to go with my 60 mm lens and Subsee diopters, and the new Nauticam housing when it all comes out.

Two clarifications: First, the pygmy was shot with a Subsee +5 diopter, while the shrimp was with the 60mm lens alone. Second, my reflection that these are "about as good as I can make with this system" is in reference to IQ, as I could clearly do better on composition regardless of system.