Probably the same type of things that have been brought up in a previous similar discussion at https://forums.macrumors.com/thread...t-iphone-x-to-remain-fast-and-snappy.2146752/ would apply again.What do you think?
they made an emphasis to increase performance on older devices with iOS 12 and it was a very public thing with the whole battery replacement thing.... I don't see them going back on that with iOS 13.... Even though it might hurt sales I think they painted themselves in to a corner where they have to keep it up now and make sure older supported devices perform well with new upgrades.
The only way if knowing is to let others install it on their phones and for you to await feedback.
I always wait a few weeks before installing big updates.