Speed regulation of a replacement fan?

[Smellydeli]

The specifications say 5000-5499 rpm. What does it mean? Does it mean the speed won't be lower than 5000 rpm even when the temperature is low enough to cool with the 3000 rpm?

From the NewEgg page, it states 4,500k to 5,000k rpm although the difference is probably negligible with such a tiny fan. The advertised speeds are probably the fastest speeds it can spin at, not that it will spin at those rated speeds all the time.

So if some fan has it's maximum speed 1500 rpm, at 56 C the speed would be 1500*0.7=1050 rpm. Is that correct or am I wrong?

The temperature of the chipset is dependent on load, voltage and ambient temperature. That 56C for example would be the idle temp while 65C would be under load. Voltage should not change during this. Fan speed dependent on temperature (if controlled by BIOS to throttle depending on temperature) or to spin at maximum speed all the time or manually controlled.

Just get the Thermalright heatsink and you'll not even need the 80mm fan as the temperature won't get near 56C under load. Don't forget to apply fresh thermal paste.