The best thing I have ever used for this is teflon or other HDPE type plastic capable of withstanding high temps. I have used teflon scrap from industrial work for a pair of washers on the pin to keep the pin bearing centered between the bosses and on the rod journal.
I don't have any scientific theory to prove it, but I'm absolutely POSITIVE the bearing takes a much worse beating when half of it is hanging out in the breeze. Half the surface area if nothing else right?
Besides, I've seen the difference myself. The particular engine I refer to would eat a top end bearing about every three months like clockwork, even using high quality german bearings. When we came up with the washers to hold the bearing centered, it stopped munching parts. Running several years now with no more failures.
I once saw the same thing in here somewhere, so I know I'm not imagining things.