It all depends on who you listen to. The 318 was never a High Performance engine till way late. But if you add all the good parts, like they did to the 360, they ran real strong. You may have noticed a "Theoretical" reason stated, like more cubes, but in practice 20 or 40 cubic inches does not make as much difference as good heads, a good carb, a good intake, enough compression (for the fuel one is going to use), a quick ignition curve, and a sealed combustion chamber, and a cam to get all of the above to play together well.