Mojave installation will change the fusion drive to APFS without option. Mine completely stopped working once that happened. I have an 850 evo on an OWC card and a SM951 combined into a fusion drive. I had to install Mojave on a different hard drive and CCC it over to the fusion drive. Works great when using Mac OS extended journaled on the fusion drive. Getting about 1500mbs up and down with the combined drive just like with HS. It confused me for a couple of days as Mojave worked fine on my backup HDD but then acted like the video card was the issue when installed on said fusion drive. Nope the APFS format of the drive was the issue. Just FYI for those of you using the fusion option.