"Correct me if I'm wrong but a temperature differential is all I need."
For the most part this is correct, the larger the diff the better for volts/ma, along with not burning up the chip
There are different schools of thought when it comes to pushing or pulling the coolant air. I'm always for pushing since it follows hot air rising. BUT there are those who say using the pull method assists with a vacuum to suck the cooler air in.
Basically it's whichever you're comfortable with, and the fan you plan on using.
IF you have an area where there even a slight incoming air leak, that's a nice use of it :-).
Hope that helps
Bruce S