Hi, Long standing Mac user in need of some advice. Some background: Machine: Mac Pro 1,1 (2006) 2 x 2.66 Ghz Dual Core, ATI Radeon 4870 512MB, 3GB RAM, Lion installed. The Mac is permanently connected to a Samsung 40 inch screen at 1920x1080 resolution. The problem: I've been trying to play various 1080p mkv files and have been unable to do so without obvious stuttering due to lost frames. Apps I've tried: VLC, adjusted various options as per some searches on the subject in Google. No noticeable improvement. Plex, tried turning on hardware acceleration. No noticeable improvement. XMBC, again tried turning on hardware acceleration, no change. What's frustrating is that when playing the files the CPU is barely doing anything so it's not like the machine is visibly struggling to keep up. So I'm throwing this out to you guys for some advice, has anyone experienced this before on a machine of similar spec? If it's not CPU that's the bottleneck what else could it be, would more RAM or a different Graphics card help? As a last resort would Mountain Lion bring anything to the table here? Kind of looking forward to the 'challenge' of upgrading if so.. or perhaps I'm just asking too much for a 7 year old Mac to be able to play 1080p? All advice and feedback appreciated!!