Than you very much for your answer.
So the big difference is the powered USB 2 SATA Bridge and idle/sleep power consumption of the drive.
Have you also done measurements of the HC-1 with no additional disk connected, just a sd card for the system?
I want to build a small server with low power consumption for usage with Nextcloud, Firefox Sync Server, Print/Scan Server, ...
The XU4 /HC-1 seems to be a good compromise between performance, (idle) power consumption and software support. (compared to RasPi 3, Odroid C2)
But as there is already a small Synology NAS running i think i don`t need much disk space in this small server.
The HC-1 with passive cooling seemed to be a nice option, but when the idle power consumption is signifcant larger maybe the XU4 would be the better option. Using the XU4 with an emmc for the system and a 128/200/256 GB microSD as disk space for local data (although the micro sd card reader should be limited to ~40MB/sec). Or some other disk connected over USB3 with less idle consumption.