It is necessary to do a test with the same hardware and software. I mean use the same brand name and model of memory, 2.5” HDD or M.2 SSD, same operating system, Chipset SATA mode. Check if the operating system is up to date on both units.
The newer version has better performance and better graphics.
Think it's not just me, I see others are also posting longer boot times with NUC6 relative to the NUC5 before we get to Intel NUC logo...
Turning off the legacy boot in the BIOS as suggested elsewhere worked for a while....
NUC6 appears to be bricked now after it entered sleep mode, separate discussion to follow.