Originally Posted by
Sixth Freedom
LHR<>SYD in CW with Gold status in the BAEC will earn you 52,826 miles, enough for a one way business class ticket to North America, India or South Africa.
Another way of looking at what "all those miles" are worth... the fare on EY essentially includes an upgrade from J to F round trip (which the OP said they would consider using on BA, if upgraded space were available). To make a reasonable comparison, one would really need to deduct the cost in miles of a round trip upgrade to SYD from those 52,826 miles earned (especially if the OP actually does MFU to F on BA in the end).
I'm finding it very hard to find a compelling case for BA in the OP's dilemma.