Feedback: I used the 1.4TC for a day, but when I reviewed the shots that night I could see some image degradation. I quit using it because of that, but I really did like the focal length. Basically it allowed me to shoot exactly as I've been doing except not have to crop. But I think a) it may be better to crop, and b) I'll just have to get closer.
I've been strongly considering a Sigma 150 macro, if I could get a port to fit.
As for focusing speed, I was correct. The D850 is faster enough than the D810 that a TC'd lens feels about the same on the D805 as the bare lens did on the D810 in terms of focus speed.
The loss of sharpness was very slight, but I'm chasing those gains.
Interesting topic - I believe I have the same Thinktank bag. And I even made a Facebook album about packing it on my last trip, in March. D850, Nauticam housing, dual YS-D1 strobes, Kraken focus light, etc. I use a bunch of bubble
wrap and a Neoprene hood to pad things, mostly. I also have a color check card in the outer pocket that provides a bit of protection.
First comment - I have to remove the upper two ball joints to make this fit. The D810 housing was even a bit worse as it is slightly taller. I use a ziplock bag to carry a small pliers to remove the ball joint and hold the removed joints, plus a second smaller ziplock to hold the 4 plastic washers at the bottom of the joints. I also carry a quarter or a small screwdriver to help mount the camera to its tray. I don't remove the lower two ball joints or the handles. I do tuck things in around the handles, like the vacuum pump and parts of strobe arms.
About half the space is taken up with a 230mm dome port, and the other half with the housing plus lots of bits.
My really first underwater camera was one of those disposable film ones. After that, Canon SD630 in Canon housing. Then followed a series of such Canon's: SD870is, s95, s120. Each failed with a zoom defect above water by the way. Then a Sony RX100 II with a pair of real strobes. Then Nikon D810, and D850.