Pessimism nor optimism have anything to do with it here, it's simply knowing football players. As you pointed out Peyton is on his last legs and Vick had 4 days of practice as the starter. But Derek Carr is a franchise QB in the making, a strong armed guy who is making better decisions with each start in his young career Josh McCown has always been a smart journeyman with the adequate tools to have big games. And as much as I despise Dalton, he has always been a good thrower with quality weapons to take advantage of porous defenses. Kaepernick is an athlete masquerading as a terrible QB who has regressed every year of his career. I don't doubt he could have a solid game with the way our defense is playing but if he throws for 400 yards, hell will have officially frozen over. If you are looking to be this big of a pessimist, it would be more realistic to think he will run all over us than to magically have the throwing talent that he simply doesn't have. We have after all allowed easy TD runs by the aforementioned McCown and Dalton and they are nowhere near as athletic as Kaepernick is.