Yes, 60gb should be fine for OS and programs, you may be able to fit 1 game on there too, depending on how much programs you have. If you use Steam/Origin, this will help: http://www.techist.com/forums/f75/upgrade-soon-but-what-252211/#post1948388
I've been looking for a laptop as well (w/ 2 drive bays), but I don't have the portability issue. I'm looking towards the G55VW...but that's around 9 lbs. A friend of mine had a Toshiba laptop with two drive bays that was pretty light...I just looked for it on Toshiba's (terrible) website, but...
Seems pretty good for its price. Hard drive is quite slow, but you get what you pay for. AMD Radeon HD 7670M - Notebookcheck.net Tech <--This doesn't have Diablo 3 on there, but you can get the general idea of that GPU.
1) You should probably blow the dust out of your case (compressed air can, air compressor, end of a vacuum)
2) My temperatures always increase when summer comes around (by 2-5 degrees Celsius), this could be a factor depending where you live...
3) Replacing the thermal paste on your cpu may...
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