I currently own the D700 and WT-4a. I usually shoot and inspect the image on my Mac, right away. The time it takes for the WT-4a to put a 12MP image on my Mac is about 5-10 seconds. It’s slow, but bearable. Power consumption per image is huge – the WT4-a battery lasts for about 30-45 minutes of work. In fact, I always have 2 spare batteries standing by.
That being said, and given the 36MP size of the D800 images, I doubt that I’ll be able to continue and use the WT-4a. Even the new WT-5a is only twice as fast as the WT-4a, and anyhow, it only works with the D4. Doh.
To sum up: there’s a need for a brand new, blazing fast, power-efficient WiFi option for the D800. Of course, a built-in solution would be the best.