i just bought a used phenom ii x6 that uses 125W of power.
now i don't have the motherboard yet, so my question is: can i try the cpu on my old board that supports only 90W cpu's? i would only test it if it work.. wouldn't do any serious work!
As long as you simply boot up into windows, no problem. The only time the CPU will demand max wattage is under stress, like gaming or running an app that operates the CPU at near 100%. During boot up and light usage, you will be fine.