@Robert Getzner:
This is great. Thanks for the detailed analysis!
And I wish there was some wiki where information like this were made permanent (Perhaps the Arduino playground?).
Until then, could you please create a separate new thread/topic on the "Storage" section of the forum, and either link to, or copy and paste, the information from your webpage.
You could perhaps title the thread something generic enough (e.g., "SD card writing at high speed / sample rate") so that future searchers can find it easily.