When it comes to a high clock dual core phenom vs a low clock athlon x4 the phenom will outprefrom it in most things. Most things still aren't made to use 4 cores.
The Phenom II X2s are great duals. The Phenom X4s are better, and have been dropping in price lately. The Phenom II X4 955 BE is selling for $120 with free shipping.