I purchased the Sapphire Vapor-X 7970 GHz OC 3 GB about a week ago and was totally dismayed and disgusted when all I could get was ~540 kh/s max litecoin mining despite many different settings and found that many others were in the same boat. After I read Sync's quote of the thread about a guy flashing the Vapor-X BIOS to the Gigabyte one and getting 630 kh/s, I figured I'd be a guinea pig.
It seemed kind of strange to me to flash a Sapphire card with a Gigabyte BIOS and after I did it, the card *DID NOT* boot for me. Luckily, the Vapor-X has a button to switch between two onboard BIOSes (which seem identical on the Vapor-X), so you can recover. If you have an onboard VGA, you can also recover/flash from that instead to be safe.
The next step was to try the Sapphire Dual-X 7970 BIOS and that was the golden ticket! All you need to is download the Dual-X BIOS and flash your Vapor-X with it (follow instructions on how to flash the BIOS from the previous link). I used this BIOS version:http://www.techpowerup.com/vgabios/129658/Sapphire.HD7970.3072.120926.html
After you restart, the default speeds are 950/1425 so I'd say since you bought the Vapor-X, it is totally safe to use AMD Overdrive to bring back the speed of the card to 1050/1500 stock.
Here's the CGMINER settings I am using to obtain 700+ kh/s total stock Vapor-X speeds. I did not try to optimize/overclock. You can if you really want:
-g 2 --thread-concurrency 8192 --worksize 256 -I 13
Here's the proof and happily mining Litecoins at 700+ kh/s now:
1. Download this Sapphire Video card bios: http://www.techpowerup.com/vgabios/129658/Sapphire.HD7970.3072.120926.html
2. Download the ATI flash utility: http://www.techpowerup.com/downloads/2230/ATIFlash_4.07.html
3. Create a bootable USB stick using this utility: http://rufus.akeo.ie/
4. Copy the BIOS and flash utility to the bootable USB stick.
5. Reboot from the USB stick. DOS type command prompt will show up.
6. Run "atiflash.exe -i" which will show you the device IDs of your cards.
7. To start rewriting the BIOS, run "atiflash.exe -f -p 0 new.rom" where you replace "0" with the 7970 card device ID if different. "new.rom" is the filename of the BIOS you downloaded.
8. When it says successful, reboot.
If you found this helpful, LTC donations gladly accepted at LhJd2L6A7hmYucxyeKHKYgkzdLDLyoAHUE
Disclaimer: While everything seems to work fine with my computer, know that you are doing something at your own risk.