If you only run 2 fans, pull is best. There's usually zero difference between push and pull in performance, but pull traps FAR less dust between fan and rad.
I'm told that if you run push-pull, you want matched or lower speed fans pushing and higher speed ones pulling. Do it the other way around and you 'spoil' the airflow, as well as forcing the pull fans to run faster than they are designed to... apparently...
"matched or lower speed fans pushing"...Aren't you supposed to run the. At the same speed?