Yes that's plenty, you'll be fine with that power supply. If you want to be a little safer you might want to get something slightly higher quality, a PSU is a long term investment anyways and an 800-1000W platinum will ensure a little more long-term stability. You might make the money back in energy savings depending on how intensively you're using the cards and if you carry it into your next build.
EDIT: NVM I didn't see "my." No use upgrading if you already have the GQ.