The statement about 20 weight being what it is in winter is interesting. SAE weights are established at standardized temps (0 and 100*C, as I recall). That's the basis for the viscosity ratings, plain and simple.
The w in 20w stands for winter and I only ment that on the inatial startup for the first few seconds until the motor starts to warm. I Made a mistake I ment 15w 40 when I was talking about the rotilla oil not 20w 50. I agee about blanket oil statements and if it sounded Like I was making one I was not trying to. Here is a link to a really good article it is mainly geared to flat tappets but stands the same for roller cams.-http://www.hotrod.com/techarticles/engine/flat_tappet_cam_tech/
If you read the charts it talks about the zddp content which is the main friction modifer in conventional oils and Like a I said before about the newer conventional oils becoming cheap quality these additive are disapering hence major bearing and cam lobe wear.