Are you asking about shutter lag or write time? Shutter lag (the delay between pushing the button and the picture being captured) is independent of the speed of the flash card.
A faster card helps when you are trying to take a series of pictures as fast as the camera will allow. But it only helps if the camera circuitry is fast enough to take advantage of the faster card.
This doesn't directly answer your question, but there is a database of flash card speeds with various dSLRs here:
You can see that on some (mostly older) cameras, a faster card won't do squat for write speed, but on the newer models, they make a huge difference.
A manual-focus slide shooter lost in the world of digicams.