can the 550d do 24fps at any resolution raw? what is the maximum resolution for 24fps raw?
960x480 24FPS works on 500D
Since 960 X 480 at 24 fps works on 500D and 600D I'm sure that 550D will handle it too

On my 600D I can shoot continuous at these resolutions:
- 720 X 720 = 0.52 Megapixel (1 : 1 aspect ratio)
- 960 X 540 = 0.52 Megapixel (16 : 9 aspect ratio)
- 1280 X 400 = 0.51 Megapixel (16 : 5 aspect ratio)
Higher resolutions will stop after a few seconds. I guess on the 500D and 550D you'll get very similar results.
Upscaling these resolutions to a width of 1920 will give you an image that looks fairly comparable to 1920 X 1080 H.264 in terms of detail and sharpness, but it'll have way more dynamic range and better colors then the default videos. I did a few comparisons and I have the impression that there's still a bit more sharpness in the 1920 X 1080 H.264 videos. But that was under bad lighting conditions ...
For those who want to do some comparisons on their own: Keep in mind that you have to change the focal length to get comparable results! Because the crop factor increases with these resolutions above. They are only crops of the sensor. Here are the crop factors you'll get with the raw resolutions:
Width | Cropfactor | Multiple of H.264 crop
1734 = 1.60 | 1
1280 = 2.17 | 1.36
960 = 2.89 | 1.81
720 = 3.85 | 2.41
So if you shoot a video in 1920 X 1080 H.264 at 55mm and you want to compare it with a 960 X 540 raw video you have to change the focal length to 30mm (55 / 1.81 = 30). At least if my math is correct

And btw. I wouldn't upgrade to a 650D if I would want more frames. The old but gold 50D takes CF cards and might be able to record 1592 X 682 (21 : 9) or maybe even 1592 X 895 (16 : 9)! That wouldn't even affect the crop factor since 1592 is the full width of the LiveView image
