360 vs 383

I do agree bore size is the main advantage of the 383, mainly cause it allows bigger valve sizes.
But to play a little bit of a Devil's advocate here, a 273 to a 400 bore size difference is 0.715" with just under a 4" being midway so basically 318/360/340. Even a 318 bore is capable of making enough hp to satisfy most even a tiny 273 can make enough for a majority of the people. So a bigger is definitely an advantage but it's an advantage most won't make use of, but for those running 400+ cid and or 600+ hp you probably could take advantage of the bigger bore.