The First Benchmarks Of Unity On XMir: There's A Performance Hit
Written by Michael Larabel in Display Drivers on 28 June 2013. Page 4 of 5. 113 Comments

OpenArena 0.8.5, which is a rather CPU-limited game and doesn't even make use of GLSL, saw no performance difference at 800 x 600 but at 1920 x 1080, the old game saw its frame-rate drop by about 25% with going through XMir.

The GLSL-using OpenArena 0.8.8 release also suffered from performance overhead with XMir.

There was slight performance degradation for the Prey (id Tech 4) commercial game when tossing XMir into the equation.