For me, I see use target size and success rate in the conditions as my judge for distance. I don't shoot primarily at large plates and feel if I, with my skill set and equipment, can hit a vital zone sized target 100% at x distance with x conditions in that position, it is safe for me to take that shot on game.
I also use minimum expansion velocity as the furthest distance for that cartridge/bullet combo.
Advances in higher BC bullets, more reliable expanding bullets, less sensitive powders, cheap accurate ballistic apps like BallisticARC, wind meters and more accurate laser range finders have made previously crazy long range shots fairly easily attainable to most people. Just look at the numbers discussed these days compared to 10-20 years ago. The absolute biggest leap in long range shooting gas come from advances in laser range finders.
These days the biggest limiting factors on effective long range shots are laser range finders, practice and wind reading.
1000 yards on a 24" plate isn't too difficult these days because we can easily verify it is actually 1003yds and with pocket computers can accurately factor in changes in temp, humidity and pressure for that particular shot. Change that 24" target to 6-8" and all the other stuff needs to tighten up more too. ES's need to go lower, positions need to be steadier, wind calls need to be more accurately guessed, laser rangefinders need to have tighter tolerance.
As the shooting shorts pushes the envelope to 6,000yrds, the lessons learned make 1,000yrds much easier.
Now if someone wants to "play" today's long range game with equipment that was great in 1980, they should stick with 1980 distances. Just because you can buy a $100 LRF doesn't mean it will help you at 600yrds let alone 1000+. For example, I run a Sig Kilo 2200MR which works well to 1000-ish but it can't even even tailgate let alone be in the same ballpark as top end offerings at greater distances.
If you reload like its 1776, calling them "handloads" does add quality for distance.
The internet, like this forum or Youtube, has been extremely helpful in educating and sharing techniques and standards. Without the internet we would only reload/shoot/expect as good as our neighbors can do.
All in all, advancements in technology have drastically shortened the learning curve but actually putting that info to the test is still REQUIRED to test what an individual is safely capable of, in my opinion.