I am quite happy with my 627 Pro. The more I shoot it the better I get with it. I am on my third set of grips with it, currently Pachmayr Decelerators, which work well enough for me but I am hoping to find something even better.
PC vs Pro. The price of a new PC will probably be around $300 more than a Pro. I think right out of the box the PC will shoot better. It will be smoother and probably sighted in better. I think if you shoot your Pro, it will probably get just as smooth over time and you can sight it in yourself.
From your post it sounds like you have found a 4 inch PC at a pawn shop. If you want to tell us the condition and price, probably lots of people here will be happy to give you an opinion if it is a good deal or not. Without ever having seen one, I still think a 4 inch PC would be a desirable gun to have.