PM? What PM?
As Bill stated, airflow is critical, and I consider it to be the most important factor. Anyone who's read through Bill's radiator roundup (at
www.overclockers.com ) knows this.
So 5C isn't impressive, unless it's a no fan setup. Sorry, no flame intended.
Copyman gets an immeasurable difference, that may be around 1 C, and his rad is smaller.
This is exactly why I've opted for a blower: massive airflow and pressure, combined with low noise. Automotive blowers seem to work well at 5 volts (hint, hint).