I use the Wyeast equivalent and recently had it plow through a 9.3% IIPA with no problem. It was done fermenting and cleaning up in 7 days.
But on a beer that big you'll probably want at least 10-20% sugar to make sure it's dry enough. Or do what Oldsock is saying and pitch another strain. I wouldn't wait until the first strain is done to pitch the second - maybe pitch it when the gravity has been reduced by 50-60%