I've got a 8120 as well, running at stock speeds. Using a Artic Cooler Freezer Pro 13 heatsink, it runs at less than 40°c during Lux renders and idles at well below room temp.

Remember to turn off turbo mode in the bios. If you don't it switches to a 4-core cpu running at a higher clock speed rather than an 8-core processor. Speed wise it is around 15-20% faster than my 965 Phenom X4. I don't think that's enough to justify the price/power premium.

Given that Piledriver is a development of Bulldozer, personally I would consider the 965 and then wait until the new Steamroller chips appear with a new socket.