Maybe I wasn't clear enough : there are 3 different interrupts. Let's call them A, B and C.
There are 333µs between every A, which is the interrupt that generate the 8 bytes.
There should be approximatively 333µs between every B, and 333µs between every C too, but B and C don't generate data.
I agree I need a baudrate > 115200 and that's what I do, it is possible to have a higher baudrate, even 1 000 000 baud works actually.
So to answer your question, yes I need to send the 8 bytes between every A.