Recently the hero Durante, known for the Durante Fix for Dark Souls 1, released the Generic DownSampling Tool, or GeDoSaTo. It allows many games to be rendered at a resolution much, much higher than originally intended, and allows the user to downsample it to whatever actual monitor resolution they have. A neat thing is that you can also take full resolution screenshots and save them, which I've done with Halo CE. Here's an example of the amazing detail we can look forward to once there are 8K displays on the market:

On my i7 4770K with a GTX 770, it runs the game at 8K at 60FPS easily, even in hectic multiplayer matches.

Here's a collection of some screenshots I took at this resolution from Campaign and Multiplayer.

The antialiasing and texture filtering from running the game at 8K is absurdly gorgeous, and breathes a tiny bit more life into an already thriving game.