The central issue here, is whether you have a buffer onboard the camera. On older and lower specced models, the fast "Camera" buffer might be small or even absent altogether. If the camera has to write direct to the card, then cardspeed will come into play (and it is also noticeably faster when being read by a USB 2.0 card reader) but I find it hard to believe that any recent camera on the far side of around a hundred quid, would not have such a dedicated buffer.
Conan