I have both, so far I had 2 Gigabyte burned.
Sapphire (Toxic) still run fine.
It seems there is a design issue with Gigabyte 280x card (same as 7970). Voltage regulators are burning. Each time the same one at the same place (and I am not the obnly one to get this).
I was a Gigabyte addict. Now I prefer Sapphire.
Happy Mining! :)