This has never happened to me before…
i7 SandyBridge 16gb RAM
During playback, if I open an Edit Window or close an Edit Window, the playback will either stutter -or- the volume will dip like 40db just for an instant and then spring back to normal. This has -never- happened to me before. In fact, the playback engine has been so utterly reliable for me I never gave upgrading a second thought, but this is a consistent behaviour.