Fallout 4 CFX profile works on my R9 390x setup since day one. Crimson 16.1 are great drivers and I have no problems playing anything. Haven't tried 16.2.
Granted I dont have a 390, but the drivers for my 290x should be the same since the 390 is a slightly improved/upclocked version of the 290 series. And I played FO4 from the day it unlocked on steam. CFX has not worked properly since launch. And there wasnt even a profile available until the 16.1.1 hotfix on Feb. 1st. Look at AMD's own driver page:
http://support.amd.com/en-us/kb-articles/Pages/AMD-Radeon-Software-Crimson-Edition-16.1.1-Hotfix-Release-Notes.aspx
[An AMD Crossfire™ profile is available for Fallout 4]
At one time, late last year after launch, occasionally people reported decent results using the Crysis3 CFX profile for FO4, but it didnt really help me.
Then, at some point, AMD actively DISABLED CFX until the 16.1 hotfix at the driver level, so you simply could not even force enable the 2nd card if you tried, so there was at the very least a time where you could not have been playing with the 2nd card fully enabled. You may have thought it was working, but it actually wasnt, even if you forced AFR friendly or something along those lines. That is certainly not flawless.
The 16.1 Hotfix came along and like the next day, Bethesda pushed out their 1.3 update to FO4 which rendered CFX practically unusable again. I suppose thats not entirely AMD's fault, but if they kept in contact with Bethesda, they wouldve known the mandatory update was imminent.
Finally, even with the latest 16.2 Hotfix, performance remains awful for me with details cranked and CFX enabled. Disable CFX and performance improves remarkably.
Oh, and my Titan Blacks in my other box have worked great in SLI since the first driver release after FO4's launch. I didnt rag on AMD back then because FO4 does have some Gameworks stuff in it, so I expected problems for a little while with CFX, but its getting sad now that they still havent fixed the problem.