Axial fans dont like pushing, but for a powerfull fan it works well pulling.
2x vahuall heatercores
172mm fan. Airflow doesnt change much with the second rad.
http://server5.uploadit.org/files/kbn2k3-rads.jpg
However I think a 120.3 setup would be quieter - fans over 120mm usually have very crappy bearings.
A 120.3 has probably as much if not more area than mine aswell.