Thank you! Well... I had no rush with finishing this video. Proxy processing was running over night, so I could start cutting the next day. Cutting worked fine in real time with ProRes422 4K clips. Then I graded just the used clips, and processing to 5.7K ProRes4444 took again all the night. But all in all I worked about 4 weeks on this video - but not every day. For the processing time I must say, my iMac2011 is surely not the best machine. E.g. a MacBookAir M1 is 3x faster here, so processing 5.7K video would be no problem at all.
For this holiday I decided to go with the Weebill S gimbal.