Since you are linking thread on oil discussion, here is one from F-Chat on motor oil:
http://www.ferrarichat.com/forum/faq...=haas_articles
Hope the article isn't too technical or contains too many words for you, but it provide a wealth of oil information.
Pay attention to chapter 9.
In summary, the thicker 60 weight oil will reach the same oil pressure as the thinner 30 weight because there is a oil pressure regulator in the engine, but the flow rate will be around 50% of the 30 weight oil as at operating temperature the 60 weight oil is double the thickness. Less flow rate at max pressure means less cooling for the engine, also, the max pressure/flow rate will be reached at a lower rpm, so at the upper rpm range the 60 weight oil will not provide enough protection for the engine.
Math, science and physics doesn't lie.
The existing M engines, the NA I6, V8 and V10 all are designed with the reduced flow rate in mind, they have extra jets of oil shooting at proper places to make up for the cooling deficit from reduced oil flow rate. These high revving engines NEEDED the extra sticky oil to stay on their metal parts.
No one said the Castrol 10w-60 is a bad oil, it's is a great oil and it can even be used in Ferrari instead of Shell oil, but it's just the wrong weight for the engine.