Push-pull usually means that there are two shrouds on the core - one on the front and the other on the back - one fan pushes and the other, well... pulls.
There are no guarantees that adding an additional fan will get you any better temps (either push-pull or stacked).
What I was doing was stacking two fans, both "pulling". This helped my temps because (as far as I can figure) a single fan at 5V was not generating enough pressure to pull enough air through the core. I could have just turned up the voltage - but I'm a real sissy about noise (at least noise from my PC while I'm trying to focus on something else).
I tried both at 7V, got about the same diode readings as with one fan at 12V, was quieter than the single fan at 12V - but still too noisy for me.
Both at 5V got me diode readings of about 2C higher, but I was getting a reasonable overclock (12.5x200) at a reasonable noise level
for me (somewhere between 18 and 22 dB).
Oh, wait - a panaflo that's 80 cfm at 35dB means the 'M' version (probably FBA12G12M) right?
I'm using the 'L' version (see
here for the difference between the two) so your results will be different from mine.
And while I'm at it - that 80cfm rating is in clear unrestricted air. A radiator, particularly one that's 2" thick is most definitely a restriction.