Really? What is the 5.7 in? Guys in the 5.7 trucks have run everything from 0w-20 to 5w-30 and 0w-40, they've never got a single code and MDS still works just as it always does. Redline 5w-30 is often recommended and it's pretty much a 40 weight from what I understand.
Code's notwithstanding, I believe there is more swing in viscosity from a 5w-20 from -20F cold start in winter to 250F pulling a trailer up a hill, than there is going from 0w-20 to 0w-40 at any single temperature. So in terms of actual harm to the engine, there can't be any.