I'm planning to make a documentary timelapse video so I would like to take RAW images to have an edge in the post processing. Currently I'm having a class 4 SD card which takes about 4 sec to write the RAW file into the card. This might be a problem in situations where I would like to have a 2-3 sec interval between two shots. In the internet I found this class 10 SD card which has very high write speeds of 45MBps. I heard that write speeds also depend on the camera, so before buying this card I want to confirm whether this camera will actually be able write RAW files at such high speeds into the class 10 SD card.
A faster SD card is always better and I would expect going from a class 4 to a class 10 to shave as much as one second off the RAW processing time. However , it will most likely not get you down to 2 seconds per shot.
As far as buying SD cards online, be aware that there are reported to be a lot of fakes out there - class 2 cards with labels on them that say class 10. Make sure that whoever you buy from has a good return policy.
Also, the Canon firmware does a lot of image processing when it creates a jpg. If you have not done so, I'd strongly suggest you experiment with the post processing work flow you will need for all those RAW/DNG images. It might not be worth the effort for most of the images you will be taking.