Thanks for the heads up, LordJuanlo. I just tried it out at 6048x1080 in Eyefinity and it's working much better natively now than it did with either Flawless Widescreen or Racer_S's FOV hack.
I no longer have the Flawless Widescreen problem with the red/injured full screen effect being improperly scaled to three screens or the Racer_S issue with mask zoom/conversation zoom being wonky. Time to pick Dishonored back up! I hadn't even made it through the first assassination yet.
I'd say it's natively hor+ now, but may need to take some comparison shots to be sure. Here are some screenshots from the new update: