Late 2013 15'' seems to have the same issues with the first and second gen of Retina Macbook Pro:s, iTunes choppiness. When I compared the demo units with non-retina Macbook Pro or the iMac there is no choppiness. Does this happen with the 750m model aswell or is it the base model only? Atleast on my Windows desktop the iTunes runs smoother than on the Retina Macbook Pro.