Interesting stuff.
Brings to mind a question, however. I have a 1923 Steinway M. Is there a source of information that tells us what frequency of A pianos were tuned to in the eras they were made? It might be interesting to have our old pianos tuned to the pitch they manufactured for.
The standard of A440 was put in place internationally in 1925, from accounts that I had found online a few weeks ago ( I also believe that is in my tuners and rebuilding book as well, as is Richards info about Hz vs Cents). Manufacturers prior to that used various frequencies in a range from about 432 to 438 prior to that ( which is why I asked if anyone knew about the frequency of my Miller from circa 1889). I'm sure some pianos from some makers somewhere were also set to A440 prior to 1925.
On my Henry F Miller in the past I have experimented with tuning from A435 and did not like it. However, my piano obviously doesn't like 440 or not so in this room at least ! So I thought why not do this tuning from A438 since more notes are relatively harmonizing with that range than 440 after the summer humidity had gone away. And we, me, I, the family, love it there. Again, as Richard points out though, we do not have to sync with an orchestra as he does.
This is a round about way of saying I don't know anything about your Steinway ! On the other hand, if your Steinway sounds great at A440 then so be it. In the case of my Miller I get various different sounds at 440 than I do now at 438. Who knows why, it could be any number of reasons from lamp shades and light bulbs in the room to the harp, sound board etc, stray strings. The thing is, if you drop it or have it dropped and don't like it then you have to pay to have it brought back up. It's not a huge move in HZ but it is a move through out the entire keyboard. Good chance with an 1800's piano that it was not ever intended to be tuned from A440, IMO.
I'm just so pleased I can't see me changing from this setting. Really, I hit on it out of laziness though and knowing that next summer it probably will pull itself back up ! And incidentally, I in no way claim to be a professional tuner, I just work on my own piano and have for quite a long time as I have mentioned in other posts along the way.