I recently bought a new SD memory card for my Nikon D800 camera to improve performance when taking raw images. Prices have dropped quite a lot since I last purchased a card: I bought a 32gb SanDisk Ultra card with a read speed of 80 MB/s for 20€. The datasheet does not specify any write speed (which should be illegal), but I supposed it would be higher than the speed of my two year old 32gb SanDisk Extreme card with a read speed of 45 MB/s.
I was wrong. Using my computer, I achieved a write speed of approximately 35 MB/s with a bunch of images as my real-world test set. Using the D800, the write speed dropped to a underwhelming 10 MB/s. To estimate the write speed, I set the camera to burst mode, stopped the time it took for the write operation to finish and subsequently divided the total file size by the duration. Since the PC achieved a better write rate, I assume that this is some compatibility issue between camera and memory card. The read speed using the PC got close to the specified 80 MB/s.
End of the story: I sent the memory card back and stick to my old 45 MB/s card, which achieves more than double the write speed of the new card in the camera: 25 MB/s. I can not make any comment on the performance of the newer generation SanDisk Extreme cards, but if anyone tries them I would be happy about a comment via e-mail.