I am running both 5x390=150Mhs (1400watts) and 6x480=148Mhs (1200watts)

While I like the 390s because its just a solid performer 30MHs per GPU stable, cool and easily OCed, it just eats watts like crazy.

The 480s may not be able to match 390s in MHs but its easily a very good powersaver.

Given savings in power bill, I don't mind my current 24.5MHs per GPU on the 480s vs 30MHs on 390s.

If you are doing home mining, the amps needed for the 390s is also higher than 480s, so with 480s you can have more rigs at home. Also, the 480 is cheaper than 390s, and has better resale value because its a new card.