I have SanDisk 16GB 400X UDMA (60mb/s), 600X 16GB UDMA (90mb/s) and the Lexar 64GB 1000X UDMA7 (145mb/s) ... after the initial burst rate (at 8fps) the number of shots I can take in a stretch with 1000X UDMA7 card is much more than the other two cards. Conclusion: 7D with firmware v2 gives better burst rates with a 1000X UDMA7 CF card than the other CF cards
what means "much" more ?
It means after the 7D buffer fills up at the initial 8fps burst mode:
with 400X UDMA (60mb/s) I get 2 more shots before I have to wait for 2 seconds for the next shot
with 600X UDMA (90mb/s) I get 3 to 4 more shots before I have to wait for less than 2 seconds for the next shot
with 1000X UDMA (145mb/s) I get 7 more shots, before I have to wait for the next shot for 1 second
These are approximate numbers based on my last week's photos taken of a running Oryx in the desert.