1. ~2 kg/cm3 at idle ~4 kg/cm3 at 3000rpm+
2. Its been covered. From a technical point of view the ester based oils are superior. Then group IV based oils and then group III based oils.
If you want to know what brands etc.. Then You can't go wrong with motul, redline, royal purple and Mobil as they market their products correctly. The others such as shell, castrol etc state their group iii oils are synthetic when they really are just ripping you off.