Not possible to upgrade using AA miles on any airline except AA. You need QF points and be flying QF code in order to upgrade (no upgrade if on the BA codeshare, for example).

PE is basically J service with a (very old) J seat -- ie. not a bed. It is a great upgrade for a short or day flight (one where you won't be sleeping in any case). SIN-SYD falls into this category (while LHR-SIN does not).