I did a few tests on MIDI performance. It will handle about 1000 MIDI CC per second. This is pretty much full DIN MIDI bandwidth, so you can't give it any more. MIDI Sysex can handle about 2000 bytes/second. These figures are just for message handling, assuming they don't do anything.
But, if sending it a MIDI message means it has to do something, this will take time and it will bog down if you send it too much. My guess is that this is true of all MIDI units – any suggestions to the contrary are probably not comparing like with like. For example, an H9 will load a program in 100-300mS (depending on the program), so there is no point in sending it 10 or more Program Change messages per second.
To go further, I can't think of any reason why you would want to send a 1000 CCs per second to a guitar pedal. You obviously can do it, but it would make no sense, and it is unreasonable to expect an H9 to handle this. It will recover when the overload has passed, so it is not crashing or locking up.
There is an issue when combining Bluetooth with heavy DIN MIDI traffic – the unit was not designed for this – in particular, it will wait until the message on one channel has been handled before it looks at the other – this may cause lost data under heavy use. Our intention when the unit was conceived was that the BT would be used for programming and tweaking, and not really used during performance. Obviously, we had not anticipated the way things would go.