It doesn’t really help, but I ran it on a Titan X. Can run on a 970 later (Need to plug it in). But the results were:
VXGI diffuse and specular disabled: 300 FPS (3.3ms) when standing at one end of the hallway and looking down all the way (default player spawn)
VXGI diffuse enabled and specular disabled: 110 FPS (9ms) in the same position
VXGI diffuse and specular enabled: 80 FPS (12.5ms) in the same position