If you flash them you will still consume nearly as much power and by flashing a BIOS the cards are never as stable as they are on default settings, so if you are getting 28.3 Mhs on each one of them by mining ethereum it is a really good hashrate.

If you need to flash them or would like to ,there are a lot of guides, in google, youtube and including this very specific area of the forum, just do a search.