While size does indeed matter, you shouldn't be drawing your gun to try to deter someone by impressing them with its size. You should only draw when in immediate fear of death or serious injury in which case you should be impressing them with your exceptional marksmanship.
It is also worth mentioning that any gun pointed at you begins to grow exponentially. A friend of mine was robbed at gunpoint while working night shift at a gas station. The perp pointed a pistol at his head and demanded cash. Later he gave a description to the police including the fact that the perp had a large caliber silver pistol. The cops caught the guy and brought him back to the gas station for my friend to positively ID. They also showed him the pistol they found on the guy...a chrome plated Raven 22! My buddy told them it sure looked bigger when it was pointed at him.
IDPA Member A00640
Founding Charter Member - Middle Tennessee Shooter's Club