I was recently trying to decide between buying a used iMac or a used rMBP for a decent power bump over my 2012 cMBP as I was starting to get more heavily involved in FCPX/After Effects/Photoshop. A close friend brought over his early 2013 15" rMBP with a 2.7 i7/16GB RAM/GT 650m for me to "experiment" with. I ran 8 tabs of Chrome (4 of which were streaming 4k videos on YouTube) while also running Aperture and iMovie in the background. Not a hitch to be found. No lag anywhere and the four simultaneous 4k videos were all running flawlessly. Needless to say I was very impressed and ordered an almost identical model used from Amazon the next morning, the only difference being my 2.4 i7 vs the 2.7 i7 I tested. After doing a fresh Yosemite install, I attempted to run a similar test on my machine and with only 4 Chrome tabs open (2 of which were 4k YouTube videos) and no other applications open I started to hit hiccups as both videos would just freeze every few seconds while trying to stream and if I expanded to fullscreen they just wouldn't load at all. I assumed at first my internet connection was the root of the issue but doing a quick Speedtest check revealed my FiOS connection was still giving me my usual 50/50 connection speed. My question being, would the downgrade from a 2.7 i7 to a 2.4 i7 yield such a drastic difference?