I'm having trouble deciding whether to get a 2.5Ghz rMBP or the 2.9Ghz one. I will mainly be using the notebook on clamshell mode connected up to Dell U2412M monitor, and I'm worried about the heat-up and whether the CPU difference will make a noticeable difference in the performance on the external monitor. I'm not a gamer, main uses are word, presentations, email, web & HD streaming (720p, 1080p), with occasional photoshop & video editing but not much. Obviously the 2.9Ghz will be 'faster' but for my casual usage of the notebook I'm not sure if that will mean much. Any suggestions?