This is the main master material that I used for most of my assets (both tileable and unique).
The material is completely modular and all the features that are not needed can simply be turned off (through a simple Switch) to be performance friendly.
The material can be as simple as a Base Color and some parameters for Specular, Roughness and Metallic (without any use of textures).
The channel packed "SRM texture" holds a Specular map in the Red channel (used as Cavity to "neutralize"/"tone down" the light in Unreal), a Roughness map in the Green channel and a Metallic map in the Blue channel.
I usually pack and export my textures in Photoshop taking advantage of the amazing "Expresso" exporter: https://minifloppy.it/portfolio/expresso/