Gotta go 3 portait
I've run the legend @3600x1920 (technically 3072x1920), but you have to use a window.
5760x1080 is way too wide - you're going to have to rotate those 3 monitors portrait if you want to take advantage of the screen real-estate otherwise you're going to be stuck with 1920x1080.
You should be able to get very close to using all your screen real-estate if you go 3 portrait with 1920x1080: 3240x1920 so you should be able to run the same resolution I ran above with your 3 16:9 monitors.
Good luck!
/C\/C\
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