Some 2 gb 380s have samsung memory that can be overclocked to rather high numbers (1700 and higher). That make this cards very good for etherium, it can be run 1000 core clock or lower with downvolt and make 25mhs with low power consumption. But there is a risk that this 2 gb cards will stop working with dag file rise.
I can confirm that. For example MSI 380 2G with Samsung memory you can easy overclock to 1660-1700MHz, but 4GB version with Elpida memory no chance to overclock.
For other brands , it is similar situation.