What is the typical added latency of using Apple's Bluetooth LE MIDI connection, versus using a (USB or Lightning) wired connection?
This is a YMMV question - as the latency is going to vary based on your configuration. For instance, the version of your Bluetooth, the signal strength and even where you are in proximity to the LE MIDI connection. These are all variables that make subtle or sometimes dramatic differences in the latency you experience. So you can check on the average expected throughput with Apple, but by using a wired connection - USB also has different versions 2.0 to 4.0 are common if your computer supports it, and Lightning is also a different variable in speed. You need to test in your own environment to see what works best for you. You are only as fast as your weakest link.