OEM is without a retail box. IE, a HDD will come with bubble wrap over the drive itself and in a ESD bag. http://en.wikipedia.org/wiki/Origina...t_manufacturer

As for the Quad core vs Dual core. This is a good article to read regarding that: http://www.tomshardware.com/reviews/...ance,2373.html

TL;DR version. You'll see a more marginal increase in performance from a Dual Core to Triple Core than Triple to Quad. Unless you do a lot of multitasking during your game sessions, Quad core isn't an extreme necessity. Of course you'll probably be more set for the future as support for 4 cores settles in.