Eli plays "not to screw up, and occasionally make a smart play". Peyton plays to completely control the game and be the main force of his team winning. You gotta remember, Peyton runs that offense the majority of the time in game - not the Coordinator.
Put that responsibility on Eli, and he isn't the same QB.
I'm not trying to take anything away from Eli, but the fact still remains if I had a choice I would without a doubt have Peyton running my offense at the 4 year point.