Hi everyone!
I came across a product in the Fab that uses additional UV channels for creation of game assets (Optimized Buildings) that also did and provided a thorough performance testing with both UE4 and UE5. In the Documentation of this project they did a comparison on the typical workflow of asset creation and the another workflow with addition of more UV channels. This product shows that they could make the assets very much more optimized through the addition of UV channels and, therefore, reducing the number of draw calls. You can further check that out through the link below if you want to see more details in this regard:
https://www.fab.com/listings/df2064d3-68c7-4156-9f18-5058c1226fcd