it strongly depends on your yeasts viability. But, with a 1080 beer it's hard to over pitch. if your smackpacks are under 2 months old i would only use one (with a decent sized starter ~800mL-1L) and save the other for another brew. if you feel the need, or just simply dont trust the yeast...
I've noticed that i too run into this "problem". it mostly happens when i brew too many, too high ABV beers that i just can't drink fast enough, responsibly that is. With myself being the primary drinker of my homebrew, it does take a while to get through a few kegs of a 1.080 IIPA. i turned...