Keep it under 62(amd spec) and you will be good. Arctic silver is good as is Arctic cooling MX thermal paste.
It is important to know that your board may well be controlling fan speed based on temperatures(and keeping it at 55). so as you overclock, it may just speed up the fan to keep you at that temp. I get about 55 with a Coolermaster 212+ on a PII 955 @ 3.7.