Which Compact Flash Memory Card is Adequate?
Your camera has a max burst rate of X, and a cache buffer of size Y, allowing a theoretical continuous burst of Z images before the cache buffer is FULL.
You cannot modify X or Y, although Canon's latest firmware for the 7D did change it's memory management (effectively expanding Y somewhat)
Your camera has a theoretical write speed capability of W, limited by the write speed of whatever card you put in the slot.
Once your card's write speed exceeds the camera's write speed, you have maxed out.
If your current card speeds are slower than the camera's write speed, you will gain *some* by using faster cards. How much you gain depends on the current differential between what you have and what the camera's capable of, and it's ability to concurrently empty cache to card and write to cache as you shoot.
I'll leave it to you to dig out the specs / details and do the math.
My guess - You *might* gain 1 or 2 additional frames in a burst. Is it worth it? Only you can decide.