Obligitory link on the topic of cooling/overclocking:
Record Attempt: The 5 GHz Project:
http://www6.tomshardware.com/cpu/20031230/index.html 
Alas, 50 deg C vs 40 deg C won't make much difference. It is good to keep those temps down, though! My Cpu idles at a cool 33-38 deg C!