Sorry but im gonna have to disagree with you here.
The card is not the issue if i can use the slower card and sit at 40fps at ultra settings with the same resolution as you with headroom to spare (render scale%110).
To get the max out of the sim the cpu amd the gpu have to compliment each other. So what CPU and Memory are you running ?
These are my settings for the Flightsim profile. There is the average fps in the screenshot as well (It records that info)