It has been a little while but I seem to remember that the 5.7 got attention for how low its cost to build was with “modular” assemblies coming from non-UAW plants and final assembly in the Mexico factory. Ex-GM manufacturing guru Tom LaSorda was given the 5.7 build assignment by Bob Lutz and he got praise for how it turned out, despite the camshaft bearing fiasco.

I think I remember that the 4.7 V8 costs considerably more.

I would like to look at the BSFC maps of the 4.7 and 5.7.
Since larger bores have an efficiency advantage my guess would be that the best efficiency “island” of the 5.7 has a lower number than the best spot on the 4.7 V8 map.