After years of being a PC user, I'm about to switch over to a mac. Other than the occasional use at iStores or browsing at a friends house, I have little knowledge about them. I was leaning towards going with the 13" 2.7 GHz but would like some advice. Currently I use my laptop for iTunes, word, excel, firefox, photoshop, and for torrents. Photoshop is the most important to me, editing on a 6 year old laptop is brutal! I play the occasional online game but nothing too memory draining. Would the 2.3GHz be enough? Should I stick with the 2.7GHz? Would it really be worth it to me to go for the 15" 2.0GHz quad core? Thanks in advance!