I updated our two 2011 iMacs 27", i7, 20GB RAM, Kepler K2100m/K4100m, SSD etc. to 15.7.8 with no problems. Downloading and creating the installer with the OCLP App felt a bit nostalgic already. Then started the setup from within running 15.7.7/2.4.1 installations from either the USB stick or the applications folder, respectively. All went smooth and patches were automatically reapplied after the installations had finished. Let the machines sit for an hour to have spotlight complete indexing and now all seems fine.