Hi, I'm a film composer. I recently got a HD Quicktime (exported from Final Cut Pro) to score too and am having a frame rate issue.
I have PC based system and the Quicktime plays back fine in standalone mode. But when I bring it into Cubase the frame rate is choppy. I did some investigating and found that it is because Cubase is seeing the Quicktime at 4 frames per second. When I open the Quicktime properties, sure enough, it's saying 4 frames per second (see pic ->http://img241.imageshack.us/img241/6601/framespsec.jpg
However, on a mac it properly shows 23.98 fps.
I tested the same file on a second PC and it shows 4fps as well.