How is the 7950 and 280x king when the 270 uses less power?
I think he is referring to KH per Watt
Yup... there are plenty of cards out there and integrated Intel GPUs that use less power... but aren't worth crap for their hashrate.
So the 7950 is still king when it comes to KH/s at its power consumption rate. Especially when you use one of Lantis' scrypt bin files for cgminer and if you undervolt with the .967v firmware.
We use rigs with 3 x R9 290 Sapphire and XFX cards. They get very hot though.