Hi all, I've recently purchased an 13 inch Macbook Pro Retina 2015 with the new Intel Iris 6100 GPU chip. It's a common problem among the new rMBP models that UI transitions in Yosemite "stutter" / are choppy. E.g. Mission Control, Switching Spaces, etc. The problem got better with the latest OS X 10.10.4 Beta 2 Update - so it seems like it is a Software/GPU Driver problem and Apple is working on it. However, the UI is still not perfectly smooth - as I was used to it on my old Macbook Pro from 2011. My question to owners of older generation 13inch Retina MBP: Is your Yosemite UI perfectly smooth? From what I've heard every model had UI lag problems when it came out - and Apple had to work in optimizing GPU drivers first. If the older generation rMBPs don't lag than I know the Intel Iris 6100 in my new rMBP is powerful enough to drive the Retina Display and the UI lag is a Software problem. Otherwise I know its a Hardware Problem (i.e. Intel Iris 6100 not powerful enough to handle the high retina resolution) and I can send the device back to Apple.