Some of you guys need to get with the times. High performance engine builders and race engineers all use 30wt or lower viscosity oils. Not to save money, but to win races and races can only be won if you finish.
So they are not going to risk there multi-million dollar budgets on a few bucks of oil. But these low viscosity oils due protect engine bearings and parts and due allow for decreased friction and more Hp.
So if Mercedes wants to spec 40wt oil great you old timers stick to it, spend more money on gas and feel good, but you are not doing any good for your engine, except maybe harm as the high viscosity oils take minutes to warm up and your engine parts are rubbing and creating high temps and increased wear.