Need help deciding on the right version of XPS 15

So I have been in the market for a new laptop for the past couple of weeks, doing my research, and I have decided that the best one for me is definitely going to be the XPS15, since I've heard the XPS 17's have a lot of heating issues and aren't really worth it at the moment. My question to the community is more along the lines of what do I need for my needs, and through looking at the current Dell deals which should I get ( I know these can fluctuate, so things could be different tomorrow, but knowing what my basic needs are would be quite helpful by itself).

I do not wish to promote the Dell website, but honestly the best way for me to do this is to just give a link to the XPS 15 website rather than type out all of the specs here for a nice wall of text.

http://www.dell.com/us/p/xps-l502x/fs

As for my needs, I am currently a student so I am going to need to purchase microsoft office, but I doubt that would have any effect on the hardware needs. I usually will watch videos online, either Hulu or Youtube, and play DVD's on it when I want.

Gaming is something I do, but I'm not overly invested in PC gaming. The only games I want to be able to play are Starcraft 2, League of Legends, and Team Fortress 2, with Dota2 being a game in the near future that I know I will want to play over the internet.

Knowing this, what would you recommend. I would like to have a computer that will not be completely invalidated in a year, though I know one can never fully future proof a computer. Also, just the best bang for my buck would be nice, since I have no idea how some things compare performance wise (like is the NVIDIA GT420 significantly slower than the 525 or the 540? Is the i7 necessary over the i5?) Any help you guys could provide me would be an amazing boon, as I have had nothing but confusion over what I should get as a final purchase.