I'm assuming you have your reasons for wanting to save uncompressed frames, so the codec question doesn't arise. Really, the first thing you should do is to defragment your drive - that will stop the drive having to skip from one area to another when playing back your video. The drive speed question is secondary to that, if defragmentation doesn't work. It may involve money as well... But make sure that your disk controller has the most up to date drivers installed.