I have been testing VXGI thoroughly and it seems that I was able to squeeze much more performance out of VXGI 1 in the 4.18 branch(30%+ more). The major downside is no VXAO in tandem with diffuse tracing like possible in 2.0. Diffuse tracing in VXGI 1 is also still backwards compatible with non- series Nvidia cards though.
It seems that VXGI 2 is hard-coded in reducing quality settings to anything usable in-game minus a 1070 or higher.