So from the reviews I have read El Capitian is lag free in the GUI. I am running a 15" rMBP and still have really glitchy switches between spaces when using the Intel HD4000 Graphics. Is this possibly due to it being a upgrade versus fresh install. People who with 2012 rMBP that don't have glitching can you give me some feedback. (Yes, I am aware it's beta...I have just heard many people saying it runs smoother then Yosemite and that is not my experience so far) edit 2... The lag between spaces seems especially bad when it involves full screen mail app. Anyone else have this?