Our QA Team has had a chance to check out the new widescreen monitor with Diablo III. I'm afraid the results aren't going to be to your liking however. They confirmed the game isn't supporting the resolution currently and that there are no plans to do so going forward. I believe the ability to use it in FullScreen Windowed mode may be disabled in the near future as well.
The game servers and client UI were just not designed for this resolution and it's likely considered an exploit, giving an advantage to users with it over those without. ATI's Eyefinity feature is not supported for the same reason.
I know this isn't going to be a popular decision to share but it's where the issue stands.
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