Hello @George_McGuire,
it is hard to tell the number of events that create a performance issue in the device, it will depend a lot on the device specifications, the size of the events, number of OUs and other metadata configurations. It would be great to hear from other implementers about their cases.
As you mentioned in this other post, the right approach would be to limit the number of tracker events, which is not currently possible. This approach will involve a big change in the way the Android app does the synchronization, but I do think it is worth exploring. I have created this ticket to explore it.