I have noticed the same problem since moving from 8 to 9. I’m using a Sony HDR-SR12 on a Sony VGN-AR730E Viao Laptop with plenty of horsepower. Granted I wasn’t able to get a clean preview playback in 8 at Best settings. But I was able to preview in pretty much 29.97 in preview. This at least allowed me to make the edits that I needed to make without rendering all the time. I was hoping that in version 9 there was a new setting or two that would help with this problem, but i haven’t been able to locate it yet.