Especially if you get ones that are UDMA7, even if they aren't 1000x or anywhere close. Reason is that the UDMA7 spec includes support for the TRIM command, which means the camera can tell the card when a file has been deleted, so it can go ahead and clear out those flash blocks ahead of time, instead of at the time you are going to be writing to it. This can drastically improve write times if the CF controller manages things properly.
That's easily worked around. Don't delete large numbers of photos on the camera, and after you've filled a flash card, write ones across every bit in every block, then format it. A flash cell must be erased and rewritten only when bits go from 0 to 1, not when they go from 1 to 0, so your computer will take the performance hit of erasing all those cells when you write 1s across every bit, and you won't have to wait for them to be erased while you're shooting photographs.
Of course, to do this efficiently, you'll need to know the flash page size so you can stomp an entire page in a single write operation. Otherwise, you'll waste erase cycles unnecessarily.
There should be tools out there to do this already. If not, you can probably write one in about ten lines of C.
