Had a 640 Pro. I don't believe it has a PC tuned action. It is a Pro Series, not a Performance Center gun. Regardless, the J frame's trigger will always be heavy and it tends to have uneven weight throughout its length of the trigger travel. So even if it was slicked up by a good gunsmith, it's not going to be like a K, L, or N frame trigger, especially one that is similarly stoned and polished.
The 640 Pro does have slightly better sights than the gutter trough on most j frames (the 60 is the other exception). But the Novak style sights aren't very precise, aren't practically adjustable for elevation, and the sight radius is very short. It's also impractical to mount a reflex sight on a J frame, which is otherwise an excellent cure for short barrel, short sight radius problems.
Overall, the 640 Pro Series is one of the finest factory J frames, but in my opinion it leaves a lot to be desired as far as revolvers go. A 2.75" Model 66 is practically just as easy to carry and a far better revolver in every respect. Unless you're not going to do anything with it, a bigger revolver is best. K, L, N frame or GP100, 4", 5", 6". It's better to practice with. It's better to train with under instruction or in classes. It's better to mount optics. It's better to hunt with. It's better to fight with.
The reason they're better has little to do with ballistics. The longer barrels are certainly better with marginal cartridges like .38 Special, but as others have mentioned, .357, even from a snub nosed barrel is "good enough" and "more" doesn't necessarily accomplish anything unless we're talking about hunting bigger game or longer ranges or something. The reason the bigger guns are better is they have better triggers, are more stable prior to the shot, they have longer sight radius, they are a better platform to mount a reflex sight or optic, they have smoother, more linear triggers, less felt recoil (slower recoil velocity), they hold more cartridges (esp. useful in training where you need to keep up), and the grip geometry tends to be favorable for most shooters, giving a better reach on the trigger and more space for the support hand. They also have longer ejector rods that will push the spent shells farther out of the cylinder for more positive ejection. The j frame compromises all of these things that make a revolver so much better. It compromises on all of this, just to make it go better with a suit.