Engine oil weight and fuel economy

[Flatland2D]

I currently have Mobil 1 15w-50 in my engine. I did this in attempt to stop a smoking problem I had only at high rpms (started around 6k). Previously I had 5w-30 which was the recommended oil, but down here in Texas it gets really hot so I went up. I'm thinking about compromising with 10w-30. Anyone think I'll gain another mpg or two by using a thinner oil? I'll do at least one more tire pressure test to verify my results, but then it might be interesting to change my oil and see what happens.