I don't understand CX valuation of premium economy for club points. Other programs reward premium economy with 200% (QF) to 400% (BA) compared to their mid range discount economy fares. CX rewards you with 20-30%.
BA has been said to say their premium economy cabins are their most profitable cabin. Maybe CX is bleeding money on Y+....in which case the should rip out those cabins.
If you are doing 5.5 premium econ to get gold.... I would switch to the AA programme - if you do 5.5 premium econ on an average return sector length of 12000 miles you will be Executive Platinum (emerald). You just need to somehow do the 4 AA flights!
On the BA programme if you are doing premium econ you need less than 4 return flights to make executive club silver.