I played on a 1 pocket GC3 at a room in Philly 2 weeks ago. It was triple shimmed to 4.5" pockets (or possibly extended rails, I'm not sure). It was the main action table front and center. This used to be the "standard" for one-hole play.
I played 5 9 ball sets on it. Both me and my opponent were playing out of our minds and running out like water. It might have been the best I played in a year.
What struck me is when a ball brushes the rail a bit, it still goes on this table. On a Diamond Pro-Cut 4.5" pocket, with its different facing angles and deeper shelf, it rejects those same balls. (I already knew this, but this particular 9 ball session really reinforced it).
Going from a 4.5" GC to a 4.5" Diamond already increased the pocket difficulty by a large amount. Now that Diamonds are the standard table, taking them down to 4", 4 1/8", or 4 1/4" pockets for one pocket play is needless imo. It makes it TOO difficult.