This is quite a tricky question in that most research, test and reviews on flash card are almost fully concentrated on CF cards. The reason behind this is probably being most users who are interested in speed are heavy shooters that require big cards and are more or less limited to CF.
Also, in real life, most camera memory interface is much slower than the actual flash card, so much so that if you are seriously interested in getting some high speed performance, you have to get a high end camera with a fast interface. That would translate into a DSLR which uses CF cards. And that is also why CF cards are the only ones with a speed rating on them. And even then, the maximum write speed seen is only about 3MB/s.
I would think you are probably looking for a more concrete answer on this issue, but I am afraid it is more complicated than that due to presence of other variables like memory controllers and interface speed in cameras.
FWIW, Here is a Table I compiled based on manufacturer specs.
CF 45x 6MB/s (Theoritical limit 16.6MB/s)
CF 30x 4MB/s
CF 12x 1.8MB/s
SD 2MB/s (10MB/s claimed)
XD 3MB/s
MS Pro 1.875MB/s (20MB/s claimed)
MMC 1.6MB/s (Max)
CF cards have to a reasonable extend proven their speed to be in the ball park of the rating. But a quick look at some of the other claims will tell you that you can throw the manufacturer's specs out of the windows, as the figures are anything but meaningful. I would suspect that they are quoting the theoritical limit of the card interface itself,
which has little bearing of the speed you are actually going to see for the use of the flash card.