"Should I change from AA to QF and if so then what would be the smoothest process for status change? i.e. how can I achieve equivalent status on QF without suffering the loss of AA priviledges? I plan to fly QF in J at least 5 times per year between OZ and Europe."

You wont geta status match but it will take you very little time to reach status with QF travelling in J. Given your example of
SYD-MEL-SIN-FRA-SIN-BNE-SYD you would get 580 status credits. You need 350 credits for Silver (equivalent to AA Gold ) and 700 will get you Gold ( OW Sapphire ). This one trip would get you close to Gold status on its own.


"As a side question, if I buy a ticket SYD-FRA-SYD in J and the system spits out something different from QF-5/6 then how do I go about mileage upgrades? Does SYD-MEL-SIN-FRA-SIN-BNE-SYD count the same as SYD-SIN-FRA-SIN-SYD? "

As long as you don't have a stopover then the mileage requirements is the same as long as all the upgrades are available at time of booking the upgrade.

Dave