We don't have a number for this – depends on too many things – what the messages are, how busy the H8000 is, etc.
If you send too many messages the H8000 will initially get sluggish, and then bog down to the point that some CC messages get lost.
Basically, you have to play it by ear. Sorry.
The next set of H8000 drivers (due later this year) will have improved MIDI over FireWire performance.
