I think you should extend you hypothesis to 2000 rounds. Some years ago it seemed to be common knowledge that S&W intended their airweight J-frame .38s to have a service life of at least 2000 rounds (+P ammo did not exist at that time). (No, I cannot provide any sort of reference, much less a link. )

Anyway, as all of us fifty-somethings remember, Elmer Keith picked this up and ran with it, testing a gun using all sorts of ammo, including some of his own reloads!

I think he had his famous gunsmith Iver Hendricksen measure the gun when it was new, as the test progressed and at it's conclusion (2000+ rounds). They found no harm to the revolver and Keith wrote the thing up enough times (in generalities, I don't recall seeing a specific, dedicated article about just this topic) that we all got the message.

Thus, we might hazard the guess that, unless your M12 has some weakness of design not present in the J-frame (seems unlikely), or your M12 has an individual flaw that cannot be discovered by inspection, it should run through 1000 rounds easily - and likely 2000 or more.

I am no engineer, but it seems improbable to me that a manufacturer as prestigous as S&W would design a weapon where the margins of safety and service life would be significantly affected by the difference in standard and +P pressures - within reason, of course. But, as I said, I am no engineer and certainly have nothing to base my opinion on - other than my own, very limited practices. It will be interesting to see what your test proves.