whats your normal room temp? as for temps changing fast, thats fairly normal, one thing to check to see how much temperature difference there is from core temp and amd overdrive. Amd overdrive monitors the internal cpu temp, where core temp monitors the motherboard sensor.
As for the noise from the stock cooler, its controlled by the motherboard sensor. Keeping the socket cool is as improtant as cooling the cpu itself for noise control. Mainly need to make sure there is plenty of air flow across where the cpu, vrm, and ram are. As for the fans, the side fan, is it below or above the gpu?
Last the windows hotfixes changes the way BD is percieved. With the hotfixes, the 8120 will be a 4 core 8 thread cpu, ie windows will try to load programs across 4 main "cores" before the other 4 "threads". Some programs benefit from this.