Hi, I am thinking about buying the new MBPr 13" 2.6 GHz and hook it up to a 2048 x 1152 external display. As a lot of other people, I am a little bit worried that the GPU is underpowered for the retina display (with a connected external monitor). This was heavily debated when the product was released, but after numerous software updates and some time I want to know the general thought from the people that own the machine. Do you think the GPU is underpowered and do you feel that the UI lags noticeably because of this? Do you have an external monitor? Resolution? Does connecting this change the performance? Is this an issue at all? Thanks!