Slightly late to the party here (only a year but who's counting).
I also have a 590 Fatboy, that's basically running 24/7.
When the card is allowed to do it's own thing it's running a little hot.
I'm using a program called Fan Control to control all fans in system.
https://github.com/Rem0o/FanControl.Releases
Also allows me to ramp case fans up or down depending on GPU temp.
For the sake of being through, I'll post the fan curve I have running as well.
It's spending most of it's time between 60 and 70c and I find a static 50% less annoying than always ramping up or down, but I still want the card to be quieter if possible, or ramp the fans higher to the prevent the card from blowing up.
View: https://imgur.com/a/R3UB0e9