Unfortunately there is not a definitive way to state it. The problem being that manufacturers do not commonly post the buffer rate or the write-to rates of their cameras, they more or less advise which category of cards or specific cards are optimal for the cameras performance based on their testing. Using a faster card (than what you are currently) will not cause any aspect of the camera’s performance to increase; the only benefit from a faster card would be if you have a high speed reader and wanted to transfer the data quickly off card to the computer. - Yossi
Yep, that really answers it - thanks for asking them, though
I didn't do it just for you; I really want to know as well. When I shot jpg on my 60D and I had a class 4 sd card... I would cap out at around 8 shots... then I got a sandisk class 10 and the thing never stopped... It was awesome. Then I started to shoot raw + jpg and back down to 6-8...
Now that I'm living the mkiii lifestyle, I don't hold down the shutter the way I used to... but I want to know that if I want to do that... then my card will allow me to do so.