After some testing with Mario Bross we were indeed able to get a AMD 7970 working with QE under Mac OS X 10.8.3 using DSDT injection method.
Important Note :
You need a working SLEEP system because a bug ...and also you will need your 7970 injected in the DSDT to have 100% support in any app....( your 7970 will also work partially without DSDT injection.. but without any FB loaded ), if you have a White o black screen after boot.. just put your system to sleep and later wake up.. it will make work your 7970.
Note: If you have problems whit the boot loader screen ( like a funny characters ) Just update your boot loader ! ( i test whit the last champlist and it work fine whit my 7970 )
Also this only work whit the 10.8.3 , the new 7***.kext can't work alone in 10.8.2.
Important: this also can apply to any AMD 7*** series GPU , just test and report