do you have a shroud? this allows for more airflow over the whole radiator.
What are your idle temps and ambient air temps?
edited my post. to answer your questions not shroud idle temps are 35c-39c depending on which core. as for ambient 22-25c in house. don't have a way to measure case temps but seem a bit cooler in the case with my 120x38's sucking the air out and 2 x 120x25 sucking the air in.