From my limited understanding, in GDC talk dev said that, VXGI works similar to forward rendering technique. More poly means less FPS. So what I understand, In big and dense enviroment, FPS will be less. I think, for large area it is good to stick with heightfield and LPV and for local lights use VXGI, since this is only option for local light’s GI. Or may be I am totally wrong 