Really interesting thread so far.
It seems you guys are the experts on skydiving/550D.
With Sony CX models there's an issue if the model has optical image stabilization, which will bounce all over the place in freefall.
I'm thinking about buying a 600D, which is pretty much the same as the 550D.
The standard bundle comes with a 18-55mm IS lens. Have you experienced problems with this image stabilization in freefall, and if so, did switching it off solve the problem?