I"m considering to upgrade my 2011 low-end 21.5 iMac for the new 27 one. How does it compare with each other? I'd appraciate larger screen, anti-glare and better specs. Anyone choosing the same option? I know some of you will recommend me to add some extras but I want to make it cheap and have a larger screen. Anyone? Oh, and what does it mean BTO iMac?