No. That’s far to random, party and encounter dependent.
What if anything does this tell us about the DPR metric itself?
Oh so your question has more to do with using damage per round as a metric and the effects of "overkill"? Ok, so yeah, objectively, DPR is hard to gauge, and it's probably not a good metric to use since it's so highly variable.
All DRP says is, if facing a target dummy of a known AC, how much damage do you do on average. That's it. It can certainly be useful, to determine what your potential damage can be, if that's something that matters to you.
But it becomes less useful in a live game, as there are many factors to consider. What is the AC of the opponent, how many hit points do you need to kill it, how many enemies are in reach, does the monster have resistance to your weapon damage?
You can't really know these factors, and even if you tracked them for 20 levels of game play, you'd have to hit upon some set standard of encounter design.
DPR gets misused a lot, I'm not a maths guy, but I try to use it when calculating whether an ASI has a significant impact in the short run, for example.
What a more useful metric would be depends entirely on what your character wants to accomplish. If you're a Fighter or a Rogue, that's
usually damage.
Should overkill matter? Absolutely. But you'd need some kind of consensus to be able to determine when it does.
The old argument about two weapon vs. two handed fighting comes to mind. One big weapon can "waste" more damage than two smaller weapons.
That can be true, but it might not be true. There probably isn't any way to truly determine it, but in my opinion, I'd say it's probably a large amount. Most monsters don't have the hit points to survive more than 2 rounds of combat, so I'd say any given monster that survives round 1 is probably already down to less than half it's hit points.