The Save to Path string does in fact take the entire path and the filename (so for example C:\Folder\Rendering.png). I’ve tried as an alternative to use the execute command function to take a high res screenshot (which to my knowledge only works with a development build). I specifically have to use the high res shot for my use case because I need to render with the custom depth to get transparency. Unfortunately running the command gives me a crash and the following error:
Assertion failed: Inputs.Material || Inputs.MaskMaterial || Inputs.CaptureRegionMaterial [File:D:/Build/++UE4/Sync/Engine/Source/Runtime/Renderer/Private/PostProcess/PostProcessMaterial.cpp] [Line: 723]