Nothing based on scientific evidence from me.
My son's pickup, a 96 ranger 4.0L, had lifter noise at a cold startup for about 40 seconds. Mobil 1 brought this to just about nil. Same weight oil and filter type was used in both cases, 5w30 and Deutsch(sp?) filters.
My wife's 96 Brinco showed no difference in engine noise at all when we switched to synthetic. It also didnt make as much noise. In her case we switched to valvoline synthetic (it's what they use where she gets the oil changed). Her engine also has much less miles on it compared to the son's truck, 40,000 compared 70,000.