You can look at Richard Lee's information on cast bullets. He made tests showing that cast bullet accuracy remains best when the pressure does not exceed about 1280 times the BHN number. But he had a 10% margin allowance, so 1400 would be closer to an actual deformation limit. So, if you load right up to but never exceed 30,000 psi, dividing that number by 1400 gives a BHN of 21. It's not that you have to have bullets that hard, but rather just that you guarantee pressure won't distort the bullet when you follow that number. BHN 16 would then be 22,500 psi, which is a fine number for target shooting. All that said, Elmer Keith loaded BHN 12 up to full 44 Mag pressures, so I think a lot depends on bore finish.
I think the quote from MB in your first post is the most sensible one. Velocities can't determine the limits for a bullet unless the bullets in question are all fired in the same cartridge with the same barrel length and use propellants with the same burning characteristics charged for the same peak pressure for the velocity in question. So velocity limits are more like clues to give you a feel for it but have no absolute meaning outside the gun and load they were tested with.
Regarding things like the polygonal barrel issue, the problem is that one person's experience may not match another's because they don't own the exact same gun. The lead high-pressure issues reported with polygon barrels are partly based on Glock recommending they not be used. Guns & Ammo concluded this was due to the rough surface left by the Tenifer surface treating process. But the EPA banned the Tenifer process, so it is no longer used on U.S. Glocks, which means that if your gun is recent enough production, that wouldn't be an issue. There have also been reports of Glocks shooting lead just fine for hundreds of rounds and then, suddenly, over the space of one magazine full of lead, getting to high pressure. My guess is that could be due to bullet sizing allowing a bit of gas bypass in the outside corners of the polygon and that when it builds enough, the bullet has too little grip on it and strips in the bore. The sudden opening of your group and/or keyholing would be your clues this process is at work. Sizing bullets 0.002" over rather than the more common 0.001" over (assuming your rounds feed OK like that) could help prevent the gas cutting. The bullet coating can also help by squeezing into the rifling corners more fully for the seal. You want, if a choice has to be made, for your bullet base to be coated well over coating the tip, though the latter looks nicer.
I think the quote from MB in your first post is the most sensible one. Velocities can't determine the limits for a bullet unless the bullets in question are all fired in the same cartridge with the same barrel length and use propellants with the same burning characteristics charged for the same peak pressure for the velocity in question. So velocity limits are more like clues to give you a feel for it but have no absolute meaning outside the gun and load they were tested with.
Regarding things like the polygonal barrel issue, the problem is that one person's experience may not match another's because they don't own the exact same gun. The lead high-pressure issues reported with polygon barrels are partly based on Glock recommending they not be used. Guns & Ammo concluded this was due to the rough surface left by the Tenifer surface treating process. But the EPA banned the Tenifer process, so it is no longer used on U.S. Glocks, which means that if your gun is recent enough production, that wouldn't be an issue. There have also been reports of Glocks shooting lead just fine for hundreds of rounds and then, suddenly, over the space of one magazine full of lead, getting to high pressure. My guess is that could be due to bullet sizing allowing a bit of gas bypass in the outside corners of the polygon and that when it builds enough, the bullet has too little grip on it and strips in the bore. The sudden opening of your group and/or keyholing would be your clues this process is at work. Sizing bullets 0.002" over rather than the more common 0.001" over (assuming your rounds feed OK like that) could help prevent the gas cutting. The bullet coating can also help by squeezing into the rifling corners more fully for the seal. You want, if a choice has to be made, for your bullet base to be coated well over coating the tip, though the latter looks nicer.