Rick67,
if you do not overclock your CPU or use a higher Vcore to achieve higher clockspeeds, than go with the standard HSF. A good replacement costs you at least 30-40$ and it is only worth it, if you plan to do serious overclocking.
I can not speak for the 2.53Ghz CPU, but my 1.8a was running with the stock HSF at 2.4Ghz. I purchased a ICH-L71 with a 4200rpm fan and that gave me 3-4 degrees less heat running the CPU at full load (in a case with excellent airflow). For heavy overclockers this may make sense, but even in my case (overclocking already 33%), I am not sure, the investment was worth it.
I know, that some people here invest regardless of the value. Their motivation is to get the last Mhz out of their CPU.
To cut a long story short: If you want to overclock and run the CPU with a higher Vcore, than post the temperatur results here using the stock HSF. The professional overclockers will tell you, if buying a new HSF is worth the investment.
Cheers
Speedy