We just started playing with this feature. It appears that overcranking and undercranking is available only when shooting in 30P or 24P, and not when shooting in 60i. Is this correct?

Also, the special effects menu gave us all sorts of options from 4P up to 30P, and then a jump all the way up to 60P. That tells me that I have a good deal of flexibility to speed up the action by undercranking anywhere between 4 and 30 frames per second. But it also tells me that my slo-mo options are limited to 60P, which is basically 50% of live-action. Am I understanding this correctly?

That is correct- only in 24P or 30P do you have the variable framerate. We have firmware upgraded F350's and to enable the frame rate from 30 to 60 you'll need to go into your Maintenace menu on page 6 (CAM config) and under Slow Motion change it from "Normal" to "Expand". I'm pretty confident it is done the same way on F355's.

That is correct- only in 24P or 30P do you have the variable framerate. We have firmware upgraded F350's and to enable the frame rate from 30 to 60 you'll need to go into your Maintenace menu on page 6 (CAM config) and under Slow Motion change it from "Normal" to "Expand". I'm pretty confident it is done the same way on F355's.

It is, and the ability to expand the slow mo to 31 through 60 has been available from the beginning on the F350.

-gb-

Bear in mind that you only get half the vertical resolution (1440 x 540), but by all acconts it still looks pretty good.
Any reason though why this would be preferable to de-intelacing in post (apart from time-saving)? It always looks a bit jittery in post de-interlacing, but I've heard that done in camera it looks super smooth - so is there more going on in there thn just de-interlacing?
Steve