Ok, so I received my refurbished 15 inch about a week ago and I'm somewhat conflicted. I love the gained performance from the discrete graphics, and I've noticed the increase in processing power with the Quad Cores, but I still LOVE the 13" profile. Price wise I'll spend a little more if I keep the 15 but overall as I mentioned before, the longevity is there with the discrete/Quad advantage. I'm leaning towards the 15", but as I said, the 13 feels great in hand, especially for a frequent traveller.
I'm conflicted, any more advice or thoughts please let me know!