this is more on ohms than watts
I bought my Pioneer 5.1 reciever planning to use the speakers from my previous system. I hooked them up and it sounded great!!! Then I started to notice that my system was over heating. So I started doing some homework. My previous system used 4 ohm speakers while the Pioneer recommends 8 ohm ."with that said". I found some Sony 8 ohm speakers on sale at Bestbuy model# SS-B1000 125 watts for $40 a pair so I bought two pairs and made 1 pair my center speaker and the other my surround speakers. I had two 8ohm floor standing speakers from a couple of years back that I used for the two fronts. Now the over heating problem is gone completly and this system rocks. I would be more worried about the ohms than I would the watts so you don't blow your system up.