Mate,
After spending hundreds of dollar on expensive fully synthetic oils and 2 engines later. I am just now using the holden supplied semi syn (ACdelco 10w30 premium semi-syn). The ACdelco oil is supplied my Fuchs.
I ran the full mineral oil for the last 7,000k on the new motor and it was changed over today to the semi syn 10w30. Research I have done (calling engine builders, performance and the like - Nationally) All pretty much say use a semi-syn for push-rod engines with hydraulic lifters. Run a 10w30 or 10w40. None recommended any thing heavier for normal driving.
Unless you plan to do some heavy driving (track days, drags etc) keep with the basic, save your money and change the oil regulary (I had mine done every 7,000klm).
But its completely up to you. If there is no issues with the motor you can pretty much run any oil.