I´ve tried bringing the clip to 24 fps using After Effects CS6 time remapping and interpolation, it actually was flawless, but of course it´s really time consuming. If we can bring it to 720p cinescope (2.35) @ 24p I´d be more than satisfied with that. It would actually be unbelievably cool to see something like that from a little consumer camera like the 550d.
I can also second that 720p (1280x720) @ 12 fps works, first try skipped frames, second try flawless continous shooting. That way you can just half the speed of the clip and use pixelmotion in After Effects to get 24p, although still not the real deal of course
Oh yes I was using a SanDisk Extreme Pro SDHC UHS-I 8 GB card with 95 mb/s (I know probably overkill, but I just wanted to make sure, that the SD card is not the bottle neck here...)