I am using the standard conf: --lookup-gap 0 -g1 -I 8 --worksize 64
I have custom modified my bioses with a HEX editor to get low Vcore values and the card to still boot. But I think with Sapphire cards you can go pretty low using Trixx also.
Here is a list of Watt/Mhash/Mhz/Vcore's I am using:
4x 17,3Mhash @ 950Mhz/0.856V = 405W
4x 18.3Mhash @ 1000Mhz/ 0.880V = 445W
4x 19Mhash @ 1040/0.900V = 460W
4x 19.8Mhash @ 1080/ 0.920V = 480W
I am not using higher setting such as 1150Mhz because it demands too much voltage
What about memory clock?
I use 1000Mhz
Yeah, I use 900 but no difference with 1000. For some reason turning it all the way down to 750Mhz actually starts taking more electricity

those are lucky voltage, they aren't normal at all, i can't for example stay at 0.920v with 1080 core, the best i can achieve is 950 core/0.950