There's no caching on write aparently (probably to avoid lost data).
So writes must be mostly dependent on class + SD reader/writer driver.
Acording to wikipedia:
Class 2, 2 MB/s, slowest for SDHC cards.
Class 4, 4 MB/s.
Class 6, 6 MB/s.
Class 10, 10 MB/s.
(this is write speed, MegaBYTE).
So... either we are getting bogus results, or our cards are a little above the quoted class.
HTC Kaiser . CM6 ......... OC@530mHz - Kitchen Watch with NTP .
HTC Leo .... CMX OC@1.19gHz, Jellybean
HTC Ace .... CMX OC@1.5gHz, ICS + Sense 4.0