Intel i7 620M vs Intel i7 820QM

Hi all.. next monday i'm ordering my new laptop from dell website, but i'm not sure about which processor would be the best choice. I could choose a 620M which is a dual core but has a higher clock speed than the 820Qm which is a quad core. I could have them basically for the same price. Considering the fact that i will use this pc both for studying (engineering) and gaming/watching movies/surf the net, which one would be the best processor to pick up?
I know that the quad core would heat the laptop and drain its battery a lot: is that very different from the 620M?
last but not least: i'm not very expert in cpu, anyway i know that the new i7 processor have a turbo-boost technology which allows the processors to overclock themselves to have a higher clock speed. Does this allows to the 820QM to join the same speed of the 620m if needed?
Thank everybody for answering me and sorry for my english