It is better to use the RX 470 to mine the Ethereum. The price is lower than the 480 and has similar mining performance.
I heard that Eliovp has modified the RX 480 BIOS and can mine the Ethereum at over 31 MH/s. But he has not made one for 470 yet.
Some people has made some BIOS mod for the 470. It seems the 470 can achieve similar results as the 480.
there are modes for the 480x also which will give you more hashes if care fully done. the price difference matters after an extend!!!
Do you mean if both are mod to the maximum, the RX 480 is still better than the 470? If that is the case, I will buy the 480.