>The biggest unknown in this estimation is the speed of writing >to the card. jec6613 suggests that, theoretically, it should >be the rated speed of the card.
Just a point of order: it's the maximum speed of the card, not the rated speed. Sandisk writes sequential raw data to their cards to measure write speed, while in the real world writing a file is a transactional affair that involves multiple read and write operations. Also, there's the efficiency in the firmware of handling those transactions. As newer, faster cards than the Extreme Pro come out, you should expect further improvements in performance, as there is room to grow in the hardware. So if you get 45 MB/s on those 90 MB/s cards, at 150 MB/s you should see 75 MB/s real world speeds.
One thing of interest is that even with Expeed 2 cameras, faster cards were still faster, with the Extreme Pro being faster than the Exteme and so on, suggesting that most of Expeed 3's improvements are mostly firmware and efficiency of the software rather than card interface hardware.