I have a question, since i didn't see this being mentioned anywhere. I recently bought a new 32GB SanDisk Ultra 80MB/s card and it seems to be very inconsistent with the write speeds, I checked and the bottleneck for the 600d is 21MB/s but my speeds are all over the place. When i start recording raw it shoots up to 20MB/s and and 3 seconds later it goes down to 10 and then 18 and it just keeps jumping up and down which averages out at EXACTLY 15MB/s in the card benchmark. what is going on... My old 30mb/s card is A LOT more consistent with it's 14.8MB/s. How so? How can i fix it? Is it the card? 
PS: before you tell me how buying a 80MB/s card on a t3i is a bad decision, i only did it because it was on a 50% discount.
EDIT: Heres a video on exactly whats happening https://www.youtube.com/watch?v=Nqu-8MkYkds
EDIT: IT WAS the card. I regret not doing any research about this. If you ever plan on buying a card look at the benchmarks beforehand.
PS: before you tell me how buying a 80MB/s card on a t3i is a bad decision, i only did it because it was on a 50% discount.
EDIT: Heres a video on exactly whats happening https://www.youtube.com/watch?v=Nqu-8MkYkds
EDIT: IT WAS the card. I regret not doing any research about this. If you ever plan on buying a card look at the benchmarks beforehand.