dual core or quad core

Im going to go to college in a few months and want to buy an apple computer. The only things I will be doing is streaming videos (youtube,netflix,etc) Microsoft word, surfing the internet, and some webcam chats back home. Very minimal in games maybe some emulators, but ill probably get a tablet for that. I might want to do a bit of video editing but once again it will be minimal. For education pricing the 2.9 ghz dual core vs the 2.6 ghz quad core is a 600 dollar difference. For me and my demands would it be smart to get a quad or dual core? My big thing is lag and I dont want to deal with it at all! Is that caused more from internet connectivity rather than the actual computer itself? The only thing i really have a ton of is music, Ive got close to 2000 songs I believe.