Nikon Canada advise me that a full buffer will always cause the D800's playback and menu functions to temporarily lock-up. Using the Lexar Professional 16GB SDHC 400x as my primary card, I am experiencing too many lock-ups - my guess is about 1 in 200 shots. And this is occurring in single shot mode, not continuous shooting. I opted for SD rather than CF cards as my primary memory because they're cheaper - now I'm wondering if I made the right decision. Before investing in another set of cards, I would appreciate your opinion. Which do you set as your primary slot - SD or CF? Is CF preferable because of its higher write speed? Any other pros and cons of SD -v- CF? Finally, a "how long is a piece of string" question - what do you consider to be the optimum card speed if you're taking a series of single shots?