I get a bit higher than 60 it seems, though I don't measure it so closely most of the time. I do cook my butts in a foil pan, which may help retain some weight with the drippings...
I usually pour the drippings out into something else (another pan?), pull/chop/whatever i'm going to do, then re-introduce 1/3-1/2 of the liquid back in, and toss the pork in it. It's loose - i eyeball it how much I pour back in, never measure. It's done when it's done kinda deal.
Still though, I'd wager that a 8lb butt yields every bit of 6 lbs cooked, so that's around 75%.
So i'd be looking at 130-140lbs raw by my watch. Either way - just make more than you think you'll need. If it's one less thing to worry about, your cook will go much smoother without you worrying if it's enough.