If you really want to get really lower temps with push/pull fans its lowering the ambient air temperature which would increase the convective heat transfer coefficient. Push/Push just sounds stupid to begin with. It's like putting two batteries with the same charge facing each other. You're going no where fast with that setup in a computer case. It would only work if you had two independent and insulated wind tunnels for each fan, you would need an exhaust with the same setup. But that's just an idea. Feel free to try it and tell me how it goes.
Take a heat and mass transfer course and you'll know a little bit more. I suggest Fundamentals of Heat and Mass Transfer by Incropera and DeWitt. There's excellent material in there on convective and conductive heat transfer as well as fins.http://www.amazon.com/Fundamentals-H.../dp/0471386502