Personally Quad not even worth it unless it an I7 .Just because something is 2.2ghz Duo core, Does not mean it equal to a 4.4ghz single core. The main purpose of a mutlicore is to use for mutli apps at the same time. Since apps are getting design for mutli core and I would not go with anthing less than a duo core. Quad Core are nice but the different is very little, because programs are not design to max them out yet. I7 has a bunch of nice features which can be used now and forever such as hyperthreading.

Now gaming Dx10 and better can be solved with a physic card.