Hi Andreas, not sure why the files are slow to process, never have an issue in LR and time is the same, they are certainly sweeter and any noise is fantastic and it locks on far quicker than the R5. In this situation forget electronic, stick to mechanical, otherwise you my injure yourself, but just keep frame rate down, the LEO should then get used to it and then over time you can revert to short bursts. It never spooked the Little owls last year even at 3m away, but with the Tawny it had to be electronic and easy to do as it was all set on a tripod with a remote, but worth doing for the huge surprise a day later!!!! I know light was a premium, but just watch the DoF, personally I think you are on the cusp here, if light falls on your side think about f/8 or 9. Any breeze will soften the gorgeous plumage so like the Musk Ox keep SS high.
On a lighter note - I will warn you now, you shoot this owl over the next few days, spending the whole day with him, you will find they are very 'soporific', so you can find yourself, nodding off during the long periods of zero action.
Good luck and think about that FP.