Yeah, I always get the biggest ones I can find. I love pulled pork leftovers. I would try to get the leftovers vacuum-packed as soon as you can while they are warm. It is so awesome to come home from a long day at work and be able to reheat a pack of pulled pork when you don't have time to smoke a fresh one. Often times, the reheated meat tastes even better.
Plus, the bigger butts cook more evenly and I think turn out better than the smaller ones. I know there have been guys here who have tried smoking even smaller ones in the 5-6 pound range and didn't have the best results.
I have had good luck with 7.5 pounders though.