That thread was 2016 and I switched to EFI in 2017. Holley made a ton of changes to the emulsion circuits of the newer carbs but never explained it. It wasn't just Holley though since other carb vendors like QF did the same thing. Even the tuners like Braswell made big changes. I never did find anyone who would tell me what the theory behind the changes was. Tuner and Mark both felt the bigger holes in the emulsion jets were counterproductive.
Mark was a big help to me in those days. He had a carb flow bench and could measure booster depression and stuff like that so his recommendations came from data. Most of the other carb "gurus" that I talked to did a lot of hand waving.
We still run a lot of carbs on the dyno these days since roughly half of the customers are still carb while the others have switched to EFI. The Holley XP carbs tend to work great for drag racing, but sometimes they just don't work. Had an 1150 three circuit on the dyno the other day and it was a mess. Swapped on a 1050 two circuit and picked up 150 hp. Both carbs were new and there was no visible problem with the 1150. Just didn't work for some unknown reason.
Back then I was doing a lot of dyno testing with my own dyno "mules" for magazine articles as well as the engine book. I had two 470 pump gas engines and a 514 race gas engine. The engines ranged from 700 to 900 hp. I probably tested a dozen brand new carbs during that timeframe. The two best carbs were a 1050 Dominator two circuit, and a 4150 flange 1050 QF with annular boosters. Both of those carbs worked just perfect on anything. The 1050 AN worked great from around 550 to 750 hp, and then the 1050 two circuit was great from 700 up to 900 hp. I kept both of those carbs and sold or gave away the other ones.
One thing I learned is that some new carbs just don't work. And typically nobody can figure out why they don't work. There aren't any obvious reasons, all of the jets are the same size, same with emulsion and air bleeds and all of that. I have a feeling that it is something hidden, maybe internal to the booster or something like that. I don't have the equipment to find it or fix it so I just tell people to return the carb to Summit and get another one.