Does the Credo not have the double tap to 100% view? that along with the ability to move around the image at 100% by simply moving your finger over the screen is huge deal for me. I shoot 100% tech camera on a 160, but even if I was on a DF I would still want this. I never trusted my DF on focus that much, and have not used the DF+ but it seems that Phase/Mamiya may have improved the focus.
On focus mask, Steve comments on the DOF are dead one. You can also get fooled by Focus mask as if you are shooting in a low contrast situation, many times it won't get enough feedback to read anything. Early morning, late afternoon especially. On a plus, in bright light shooting it's a great tool since here it's much much much harder to read anything off the LCD such as critical focus. The Mask paints as green over areas and can be seen in any light. I find myself leaving it on most of the time as it just give the user one extra bit of feedback.
My ideal solution, (don't ever think this will happen) is a focus peaking live view solution like on Sony. I know many hate the A99 viewfinder EVF design, but I love it. I carry an NEx-7 around with me in the field when carrying my 160 as I know there will a shot I won't be able to get either due to time or setup any other way. Being able to dial in around the peaking for me is great.
In my experience, I don't find the Viewfinder on the DF all the bright. Sure it's large but I have never been able to get very critical focus when using it alone. I carried around the view finder magnifier for along time. This helped tremendously when trying to get critical focus with the DF or earlier Mamiya AFD bodies. I am near sighted and thus prefer the use of any tools like peaking.
Guy also hit it on the head in spades on the differences on the CMOS and CCD files. The D800e seems to have this much worse for me than my Canon's with the stronger AA filters. My biggest problem with the D800e is getting a file that has smooth transitions and not a "crunchy" look. I am finding that Capture One right now seems to do a better job many times than LR on the 800 files. But this is personal preference.
I would have loved to see focus peaking on the D800 in some form. :-)