I've written a userscript to make Twitch.TV stream pages a bit friendlier for higher resolutions. See the attached screenshot.

Features:
  • Larger video object (without popping out). The size can be controlled through the "Plus!" menu at the top of the stream page.
  • General style improvements, with the goal of making a stream page friendlier to those using "higher" resolutions.
  • Built-in script updating.
Note: Tested with 1680x1050 and 1920x1080... might not look great at other resolutions.

Userscripts.org link (bit.ly due to an ESR bug)