A lot of people think that heavier is better in terms of oil weights, and that it will offer more protection, but the thing that you have to keep in mind, is that during a good part of an engine's life, the oil is not at operating temp, and this is the area that you really want to choose the lesser of evils in.
Also, while we certainly need oil pressure, more is not necessarily better, while more oil flow is always better.
There is a great article on Ferrari chat that I have linked below. If you'd like to kill a few hours reading this, this is some excellent information in it.
http://www.ferrarichat.com/forum/faq.php?faq=haas_articles
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