Check:<BR>
 - How much RAM it uses<BR>
 - How much texture + GPGPU memory it uses<BR>
 - Minimum frame rate / Current frame rate * CPU speed * SpeedUpFactorOf(minimal number of cores you can use)<BR>
 - Similar equation for GPU calculation units<BR>
 - what level of opengl/directx/cuda your game engine requires from the graphics adaptor<BR>
 - how much disk space the installation + user info takes...<BR>

Also test on various hardware configurations.