Whatever you do, don't go out of your way to increase the clock speed to 2.8 GHz. You will not be able to tell a difference if you used a 2.6 GHz Macbook and a 2.8 GHz one side by side. In fact I'm convinced Apple don't even do anything. It's a waste of money and it just shortens your battery life.
Long story, I bought a 13 inch pro retina a few weeks ago (2.4 GHz/8GB RAM/256GB Flash) and exchanged it because of the spec bump Apple did a few weeks ago to (2.8 GHz/16GB RAM/128 GB Flash). What have I learnt? The clock speed on a CPU means nothing. Furthermore, a pretty significant disadvantage, the battery life feels a lot shorter! I'm not joking, my battery on the macbook I'm using now is a good hour less than the one I was using a few weeks ago. Right now I'm just about doing light web browsing, some reading, and watching a few YouTube videos and my laptop is dead within around 8 hours or so after a full charge. Perhaps I've got a defective battery or the flash plugin I'm using is very power hungry – but either way I'm probably going to return this Macbook for the standard 2.6 GHz clocked model.