I've been shooting the Nauticam D800 now on a couple of trips and like it a lot. Very balanced, really light in the water. It works much better with the 9" Zen glass dome, than with the 8.5 acrylic dome, as it twists in your hands (like most any DSLR & plastic dome). I really like the lever to change the ISO. They have reduced the number of parts from the D7000 quite a bit and many have been beefed up in their design. Seems to shoot well vertically as well as horizontal - one of my tests.
The Aquatica does have a couple of advantages, particularly for those that shoot video. It has controls for both function buttons! You can program these to do many functions, but one very cool thing is to use them to do motorized aperture changes! The housing is very intelligently laid out and quite rugged, we like the finish on them and the large knobs and handles. Great cold water housing.
Seacam is an awesome platform, very simple, rugged and balanced. Easy to shoot verticals as well as horizontals. Great selection of ports and accessories like their pole cam remote system and one of the most powerful TTL strobes available. The issue is right now that the housings are backordered out a couple of months.
I have to say I'm in love with the Sigma 15mm FE on this body. Tack sharp and works nicely with the Kenko 1.4 TC to make it a 21mm. I tried shooting the Nikon 16-35 f/4-5.6 and found it was just too slow uw to catch focus consistently. I'm not recommending it at this point. Maybe in bright daylight, clear water - which we didn't have. My buddy had the same issue with the Nikon 17-35 f/2.8.
I did see last night that Tokina has a 16-28 f2.8, that has very good ratings, reasonably priced and focuses to .9 feet. Either that, or I'm really reconsidering a 35mm prime lens. May rent a couple of ideas for the next trip.
Jack