I have experience with this. At my home room, Drexeline Billiards in PA (now closed unfortunately due to the whole shopping center being torn down last year), we had 20 new GC4's purchased in 2001 or 2002. They all played great, the whole time until the room closed in 2022. Before that, the room was open since 1989 with older GC 1's and 2's, that also played great. I played in this room daily for 20 some years, and knew all the tables very well.
The room always had 2 triple shimmed tables for one pocket, about 8 double shimmed tables for 9 ball players, and the rest were the factory buckets for the bangers in the back of the room. All the tables played great.
In about 2015, the owner wanted to make the one pocket tables even nicer for us. Tons of one pocket played in the room. He had the 2 triple shimmed tables reworked with new cushions and extended rails, so the extra shims would be gone. He had 4 total tables reworked this way, rather than the 2 prior triple shimmed. The mechanic used the Diamond Black cushions. (To add, the superspeed cushions were still playing like the day they were new, they were not bad, the owner just wanted to give us a "no-shim" table)
The tables were ruined. They banked much springier than all the other tables in the room that still had the original super speed cushions. They were NOT as fast as springy as the same cushions on the 7' Diamond Blue tables. They were NOT as short as the same cushions on the 7' Blue Diamonds. But they were noticeably springier compared to the SuperSpeed.
Yes, we still played one pocket on these tables. Yes, we still gambled our brains out and had a nice time. But the wrong cushions were installed. SuperSpeed would have been much better.
IMO