I own a previous generation late 2009 Mac mini c2d 2.26 ghz with 2 mb ram. I use the latest non-beta version of XBMC and have my libraries on two external usb2.0 external drives. I use a mini display port to HDMI converter. Playback of 1080p movies is flaky. Sound is perfect but it appears frames are missing and the video is choppy. Everything is fine when I set video output to 720p. Can anyone help here? Do I need to upgrade my ram to 4 Gb? Or is the speed of my external drives the bottleneck here? Thanks in advance.