Bigwoof, your user manual should indicate the best oil and also the quantities that is needed. As you mentioned about the debate of what oil to use, especially here in SA. Its a endless debate, what I can say is, whichever oil is been used, regular oil changes is still the winner.
I'm not to sure with your engine, I don't know the 2.2 very well. But when I had the 145 I used to use the Castrol Edge 5W40. Worked brilliantly. Since having the GTA, I now use the LiquiMoly 10W60, but only because Alfa specify that grade oil. We have found that with the bigger bore engines we use less oil using the LiquiMoly as oppose to the Castrol.
Both these oils are fully synthetic.