I’m having the same exact issue. XDCAM footage (1080p/23.98) stutters noticeably when it plays back on MC4.0.5. The stutters is equally bad whether the media plays back via AMA or if its been transcoded to Avid media files (MXF) via one of the DNxHD codecs. The media lives on an internal sata drive on a MacPro. And I’m certain the problem isn’t with the original footage because when I play back the same footage in FCP there is no stutter.