Yeh 1.7 is pretty good.
If I go CBR 1.3 it kind of stops.
Used a nice SD Scandisk card too.
It also has trouble playing back the file at those rates in the camera but is fine once on the computer.
Maybe the 7D and 5D can because of its dual processor thingy.
The other thing I was messing around with is shooting at 4fps with Magic Lantern.
Its like a real quick way of making a 1920/1080 timelapse video instead of images.