An easy way to do this, if you can dedicate the whole computer to just capturing the movie, is to setup a ffmpeg screencast, where you basically are capturing your screen to a movie. I've tested this, and it works pretty well. I don't know if you will be able to attain a 60 fps rate, but it's worth a try. See screencasts with ffmpeg
for a step-by-step example.
UPDATE As I sat and thought about it, the screencast example uses the mkv video format, which has a very useful trait... you can just concat them together to make long videos out of short ones. So... to avoid your excessive saving of frames to disk, you could save say 10000 frames at a time, and when the counter hit 10000, you make one mkv movie segment, then discard the old frames and start another 10000. At the end, concat all the mkv's into one movie and convert it to mp4, avi, or whatever you choose.
Ideas come to me in spurts, sorry I spread my answer out over 3 posts. :-)