Bad news. As expected, the bottleneck is the SD controller inside 550D ! I tried with a Sandisk Extreme Pro Class 10, 16Gb, 95Mb/s : same results: max res without skipped frames is 960x408 at 24fps ! Sorry boys ! However a great achievement !
Bad news 2 : when playback the latest movie capture, my 550D shows a messed-up flickering screen then no more commands are accepted, you must switch off, but red led is on, and if you switch back on, camera is frozen with red led on, you must put out the battery and then reinsert it, then switch on again and all is ok. Do you experiment the same problem ? How to solve it ?