I think it depends a lot on how they play. Warrick Dunn was a smaller guy but he was so quick he almost never took a full hit. Desean Jackson is a smaller guy, but he too is very good at seldom putting himself in a position to get smacked. Same with Wes Welker. To answer your question though- if put in a situation to take repeated hits and abuse yes a larger player will generally be more durable.That is the biggest reason Manziel's size is a concern to people. It has been proven a player doesn't have to be a giant to play QB, but Manziel's playstyle leads himself to taking a lot of hits and many feel he isn't big enough to absorb them at the next level.
I think with QBs the data about being light is pretty solid, or was a few years back, on how it adversely affects your ability to stay upright. I think 215 was the magic number there. For any other spot, no it is hard to say because how guys play at the same spot is very different – think the difference between Brooks an OLB and Ware also an OLB.
RGIII will never be the same again. I dont care what anybody tells you. He’s an example of a slight scrambling QB with ELITE speed that has fallen to injuries. Since he’s been out of the clink, Mike Vick has yet to play a full season of football. Smallish. Pass and read defenses first is always going to be the recipe for long-term success in the league.