In my experience, loading hot vs. mild, and stringing shots vs. letting the barrel cool has less effect on barrel life than the type of rifling. We all want it to last longer by running less powder, but it doesn’t pan out. I ran low node in my 6 creed barrel last year, 40.0grn instead of 42.5 max, ~6% reduction in powder. The benefit wasn’t barrel life, it was spending 6% less per shot. I got to 1,000rnds and had to add a half grain to get back over 2800, and was running a full 220fps below my starting speed for that load, and losing 30fps per match.
Similarly, I had a 6 Dasher bench rifle which was fed rounds as fast as I could during my favored wind call as well as a 6 Dasher specialty pistol built as hunting rig - lots of time between shots, and I’m not sure it’s barrel ever even got hot. There wasn’t 500rnds difference in life when they both went down. One went down in 2 seasons, while the other took a decade, but they still went down around 2500. I get similar barrel life before accuracy and speed loss with Service Rifle barrels as I do 3 Gun barrels - I just replace the Service Rifle barrels at a higher standard of precision than I had to with 3 Gun rifles.
If a given barrel goes 500rnds longer than another like it, I chalk it up to fluke before I would believe the improvement was intentional by some trick.
I have a few borescopes, they can tell you when a barrel looks terrible vs. new, but can’t tell you when the barrel is toast. Your chronograph and targets will tell you when the barrel is done. Some terrible looking barrels have shot lights out. It’s also only qualitative, whereas a guy can seat a bullet to find the lands and actually measure their throat erosion if they were so inclined.
But ALL of that said - I took the barrel off of my Seekins match rifle this month at 1440-1480rnds because the speed was falling. It was still shooting 0.6-0.7moa groups at zero day for its last match, and it killed my buck last month without argument. I could have left that barrel on it the rest of my life, and my son his life, and it would have been a fine deer killing rifle, more accurate than most any big name factory rifle on the shelf. But the barrel was absolutely trashed for my application... the good news - most barrels I just toss, but the attractive spiral fluting on this one will make a nice lamp.