Is $180 worth it to upgrade the base 27" iMac to the i5 processor? This is not the quad core. I thought the turbo charge might help me -- I am going to be commuting to a school for engineering and would like to work on projects using AutoCAD for Mac when I am at home -- but I am also on a budget. It would be ~$1700 vs ~$1900...the quad core is ~$2000 but with tax might be more. Thanks!