On the restart, mine stuck at 'preparing to configure Windows' for some 20 minutes or so before the percentage count started. Seemed to run at normal speed after that. Took over 45 minutes from starting the download to finishing the install. Seems to have installed OK (eventually).

Cumulative Update KB4074590 Windows 10 v1607 Build 14393.2068 Feb. 13-14393.2068.png