MIDI currently does not have flow control so you just need a buffer big enough to handle the incoming SysEX and the speed to process it fast enough so that the buffer does note fill up.

From what I understand, when people start implementing MIDI 2.0 (the spec was ratified in 2020) ,  this will change as MIDI 2.0 will have full duplex communication.

Right now, I don't know if manufacturer that has implemented MIDI 2.0.