Footage from my 5D and T2i play back buttery smooth, its only when I drop 70D footage on the timeline that playback becomes choppy and frames get dropped. Why is that??? I've updated my graphics card drivers and even installed the latest version of KLite codec pack (not sure whether it was even relevant).

Weirdest thing is that other people don't seem to have this problem, even on lesser powerful machines than what I have.

Any ideas to what the problem might be?

I guess I'm like the rest of them. I have not see that. I do shot in All-I.