"IT... dropped off more" ? Which dropped off more? You are missing the point. The Motul 300V 10W40 was one of the best in the test. The 5W40 showed a higher amount of loss in viscosity. Will the 5W30 be among the best or the worst. Who knows. Apparently every different blend of the same brand can test very differently.
i was trying to explain to you why the VI dropped on the 5-40 more than the 1040.. let my clarify. each oil uses the same base stock. (esters in 300v's case) the difference is the molecules that are added to each one that change shape to do heat. (contract when cold) the test used to get the Viscosity index is called the HTHS test. high temp, high shear test. the oil and apparatus are heated and the test is ran. the lack of zinc in the motul (only 1047ppm vs 1600 in amsoil) leads to more metal to metal contact. which leads to even more heat. that cause the oil to break down faster. it just happens that the molecules they use for the 5 40 weight are more susceptible to these conditions. Add sinc and phospurus to the mix. (zddP) and it will COMPLETELY change the test results. this is indeed the best route to go as Ester base stocks are hands down the best. even new grade 6 oils arent as good.
thats what my analysis has shown anyways. take it for what its worth.