I haven’t looked into it yet, but my guess is that for VXGI, SFR SLI will be very similar to VR SLI: both GPUs voxelize all geometry, and only screen-space workload is separated.
By the way, in the recent versions in vxgi-dev branch, you can see the time it takes the GPU to process world-space and screen-space VXGI workloads if you type “stat unit”. The FPS counter is not to be trusted though, because enabling stat unit adds a CPU-GPU sync and reduces the FPS in that branch.