Please watch the video : Magic Lantern 550D Raw Video Tutorial on YouTube
It's give a good explanation.
Your card is good, surely enough speed for RAW on 550D.
The result, if we compare with H264 is noticeable.
The workflow is not easy but with so many choice of utility (Rawanizer, Son of Batch, Batchelor, Raw Magic, etc) give a lots of possibility, in Windows, Mac or Linux.
Many article in forum of Magic Lantern also. Take your time to read
