This past weekend I had tried playing some of the 4K videos on You Tube that are popping up. The Verge mentioned these videos would lay most Laptops to waste and they were right as my Late 2013 base 13" rMBP basically just froze up when I attempted to play them. However last night I was able to actually play these videos on my new 2015 rMBP which is rather maxed with i7 16GB Ram and a 512GB HD. Curiously they had a fair amount of stutter using Chrome browser but were virtually glitch free if played in Safari. I'm amazed they played at all though.