I find this to be an interesting subject so I just might write a book here. I'll probably hit both sides of the discussion before I'm done.
There is a standard for pocket size and I'm not going to look it up right now. I'll just say it is more generous than what you folks are saying you want.
However the thread is about what size should be used in pro events. I'm not sure what size it would be. I'm going to mention a size below here but I'm not positive it is the size I'm going to describe, so if I say it wrong just tell me what size I'm really talking about, I think I can describe it. Pockets for pro events should be big enough that there is a minimal margin of error on hard hit down the rail shots. Seems to me this has as much to do with if not more to do with how deep the drop off is in the pockets. When I say 'minimal margin of error' I do mean very minimal. If there is no margin for error and requires the shot to be perfect, it eliminates the shot. The general rule, 'if the safety is equally difficult or more difficult than the shot, take the shot'. If you take away at least a very minimal margin of error you increase the number of safeties significantly.
So here is the problem as I see it. If you make the pockets big enough to give this small margin of error on down the rail shots, then the pockets are so big that normal (not down the rail or hit slowly down the rail) are to easy. My solution is make the pockets small enough to make the normal shot not automatic and make the depth of the pocket drop off shallow enough to give a slight margin of error on hard hit rail shots. I think I talking about just slightly smaller and slightly less deep than the standard GC4.
First off, one easy thing to figure out is the absolute minimum size. What is the smallest size that should be considered? Aren't the balls 2 and 1/4 inches in diameter? I think they are so there is your absolute minimum. 4 and 1/2 inches. Two balls wide is the absolute minimum. A shot past another ball sitting to the side but in the pocket should be difficult but possible to make. So that is what I think would be the absolute minimum, two balls wide, 4.5 inches. We are talking pool here, not snooker.
Second, what is the maximum? The size of Texas? na I don't think this matters much cause were are not really talking about that but for the purpose of this let's say 5 inches. I think that was the largest of the choices above anyway. What we are trying to discuss is, for the pros, how close to the absolute minimum do you want to go?
I would say just slightly above the minimum say 4 and 5/8 to 4 and 3/4 inches. That would keep it small enough to make sure the pros aren't just snapping them all in the pockets.
What do I mean by snapping them all in the pockets? The answer to that is probably why this is prominent on my mind this morning. Yesterday I emailed my friend to say, 'are we still on for going to the pool hall after work?' His reply was, 'I forgot to put my sticks in the car. Lets go to the VFW instead, that way I can stop at the house on the way and get my sticks.' So now instead of us going to the pool hall and getting some good practice, we are going to the VFW to deal with putting quarters up. When I get to my turn to play I put my quarters in and keep the table for about 11 or 12 games, don't remember for sure. So what is it that I don't like about this? I know it is coming. Some player that couldn't run 7 wide open balls and then the 8 ball on a 9 footer with good pockets if their life depended on it, is going to beat me. Why? because of buckets. (one of the reasons I quit bar box league) I mean this table is so easy that if the opponents balls are out of the way I don't even have to think about what order I'm going to shoot them in. Just pick one and go, leaving the black one for last. When you get down to 3 you might make sure your going to have an easy shot on the 8. Once last night my buddy said to me after a run out, 'why didn't you shoot the ? ball instead of the ? ball, it would have made the rest of it easier?' My answer was, because I would have had to walk around the table to shoot that shot next. It just didn't matter. On that particular table I could have had the opponent tell me which shots I had to shoot next and he still wouldn't have got another shot. (maybe a slight exaggeration) I had broke without making a ball, he made I think 4 or 5 of his before he missed and everything was open for me. You combine that with big pockets. With these pockets it was like playing horseshoes, you only needed to be close. Believe me, I'm not bragging about my playing here, they were just that big.
Anyway, that is what I was talking about above when I said 'snapping them all in the pockets.' You give a pro a 5 and 1/8 inch pocket and he doesn't even have to be concerned if the ball is going into the whole. You make the pocket 4 and 3/4 inches and the pros aren't going to be walking up to the shots without making sure it is going in the whole. It doesn't take much.
Another issue....You can make the pockets to small to be able to get a rhythm going. You make the pockets only 4.5 inches and the shot clock must at least be increased to 45 seconds. You make the pockets 4 inches and the shot clock must be eliminated all together.
That's all my thoughts at the moment.
Later