I apologize if this has been asked before, but I could not find anything specific to my question. I currently have a 2011 27" iMac with 2GB 6970M GPU. I was considering switching to either a MBP or rMBP with the 1GB GeForce GT 650M GPU and using an external monitor. I feel comfortable enough in comparing the other components, but not sure on how the two GPUs compare. I love my iMac, but would love the ability to take my "desktop" on the go without sacrificing the performance.