I've read several places that you can expect smoother UI animations on the 13" because the integrated graphics on the 13" is better than on the 15". Is there really any merit to this? Is really the integrated card the bottleneck of UI animations on newer Mac models? In that case the 12" MacBook should be a laggy mess, but my girlfriends is smooth like butter. On my 13" TB iTunes has some laggy animations when opening an album folder in album view. I've presumed that is caused by bad code, not by limitations on the graphics.