Tranfer rates are determined by the weakest component in the path and I do not believe that the camera tech/hardware is able to push data at those rates (yet and probably intentional). This greatly diminshes the memory card rating importance as the specified transfer rated are not (and probably never will be) achieved in actual usage. There is probably not that much difference in use between a mid level and a high level card (say 60 and 100 MB/s)
Also the manufacturers tend to exagurate (a little) and actual vs. theoretical in real world scenarios are (quite) different.
Some real world testing here.
The fastest camera / memory combination I saw during a quicl look was the Sony A=900 at 35.5 MB/sec. Thats pretty fast. The Canon 5D MK II manages 32.6 MB/sec. He did not test any cameras with SD memory.
For flash memory, CF card to computer transfers were tested 97.3 MB/sec with the fastest reader and cards.
SD memory doesn't really come close, with about 25 MB/sec being the fastest card to computer.