same here, unless i had major leakage or bearing or lifter issues i would stick to 5-30 or 10-30

Even at the point, an additive is probably better than changing viscosity. The additive will do so, however will add conditioners and other benefitical things as well.

I had 154,000 miles on my old SSEi, and still ran 5w30 winter and 10w30 summer, it still had GREAT oil psi even at hot idle, did around 30psi fully warmed up at 700-800rpm.
My current SSEi at 112,800 has the same pressure as my old one did, only 40,000 miles difference.
I've heard of people running thicker viscosity oil in an application were the engine is so worn out, it isn't producing enough pressure at idle, but thats about it.

I had a conversation with a GM engineer at the store a couple of months back. He did engine testing, and said that in their tests the Valvoline 5w-30 came out on top...Penzoil on the bottom. He added that none of the 10w-40s passed the tests, regardless of brand.