Currently Online 
For these who are interested in the transfer speed via LAN cables: it is faster than expected.
The first estimate for transferring the ~800 GB data of my PS4 to the PS4 Pro was 8 hours, but the remaining time has gone down after the first 150 GB to 3 hours. The current transfer speed is 4.2 GB per minute / 25 GB every 6 minutes (both times stopped)... that's 250 GB per hour or 1 TB in 4 hours.
Much faster than backup + restore with an external HDD or redownloading from the internet (if you don't have very fast internet). With my internet speed (100 Mbit) it would take 17 - 20 hours to download ~800 GB data.
Of course re-downloading from the PSN and re-installing by retail discs have also advantages: they can be done in the background while using the system.
Therefore I take a mixed approach: I first deleted the installations of my (few) retail games and a few of the biggest digital games before starting the transfer, otherwise the transfer would take 6 - 7 hours instead of 3 - 4 hours. After that I will redownload and reinstall the other ~600 GB data in the background while already playing the transfered games.
Edit: 400 GB to go, estimated time for that: 104 minutes... so ~4 GB per minute.
Edit 2: Another 150 GB in 41 minutes... so transfer speed has gone down to 3.7 GB per minute:
Edit 3: Data transfer of the 800 GB (729 GB games and ~70 GB settings, screenshots + stuff before that) finished in 3.5 hours... and P.T. still works ;)
