So i have an SLI dual monitor setup and noticed i had lower fps than i had when playing with one graphics card and 1 monitor, quite substantial actually the SLI setup has 180-220 fps with the same settings; the 1 monitor 1 card used to be around 270 fps
now i figured out that when i start overwatch with the second monitor turned off i do get the full 295-300 fps and they stay there even if i turn the second monitor on again
just though somebody might want to know this
tl;dr: dual monitor makes ow lose a lot of fps, start with only 1 monitor on and it’s fine
edit: it’s especially pronounced when running twitch on the second monitor