AM3 CPU's are getting sparse on the market now but something in the area of the Athlon II X4 640 is an OK choice I think. While rated at 95W it doesn't draw too much power in real practice thanks to not being burdened with a lot of cache, and if necessary it's easy to just dial down the top frequency a notch. If using AMD's own software control for that it means stepping down from 3.0 to 2.3 GHz, with further tweaking of power states possible through the K10STAT software if necessary. AM3 CPU's aren't coming back in stock so it's either getting something right now or saving the money for later. Having four cores is nice though I'll have to say, having settled for the Athlon II X4 640 after initially aiming for a Bulldozer. Then again this CPU is more expensive today as it's disappearing from the market altogether.
Thanks for your advice!
What you're saying is that the L3 cache in the Phenom's will draw considerable more power even if they're rated 95W as compared to the Athlon II X4 640?
I'm running Linux and new to undervolting, but I'm almost sure there are tools available.