Ok, so the issues I was seeing with Nvidia seem to stem from having a dual hybrid GPU setup on my PC (AMD & NV, with AMD as the ‘primary’/output card), which seems to have made the NV driver do some weird stuff. In single-GPU setups we are seeing the same improvements as on AMD. Sorry for the false alarm! :eek:
As of why UE4 is not way faster in Vulkan, it’s a matter of changing how the renderer talks to Vulkan. To do so the best way for Vulkan, D3D12 & Vulkan, we’d have to basically break all the code and rewrite it, which is not feasible as it would break licensees and marketplace. So instead we do small changes/deprecate code paths, and slowly get there. But that’s the end goal, to have a fast renderer 
4.20 is almost free of validation errors, so it has a lot of fixes.