Im looking at purchasing a 27" iMac. I'll be running a Virtual Drive such as Parallels with heavy programs such as AutoCAD, Revit, Photoshop etc. but will also be using the Mac platform for music, movies, online streming etc. Which upgrade do you think would be better for the Quad-Core iMac, upgrading to the i7 or upgrading to 8gb RAM? Thanks in advance.