I think 2 packs of US-05 will get you there. But for beers in the 10%+ range, I prefer to start with a beer in the 1.060 range, then rack onto the yeast cake for the big boy. Having a fresh, big pitch that has develeloped a bit of alcohol tolerance will rip through even the biggest beer pretty reliably.Thanks.
I'm still working on getting my head around what seems to be a contradiction. We are always counseled to "pitch plenty of yeast" for big beers, because what you pitch is only good for 4 or 5 replications/generations, but people regularly use and re-use what essentially is recycled yeast for beer after beer.
the number of generations you can go with a pitch of yeast is dependent on your sanitation and storage methods, and your tolerance for genetic drift. 4-5 repitches is generally pretty safe, assuming good sanitation.
The concern with pitching rates is that you want to control the amount of reproduction the yeast do in your beer because they produce many of their flavor compounds during that reproductive phase. This is all very backyard science-y and not at all really accurate to what's going on but the effect is at least repeatable.