I've not flown them - but I'm seeing ex-BNE BA PE for around $3500 end of June. Had a friend book this last week (end June to end July trip) and with the BUPA discount, it was around $3k. Given it's QF to SIN or HKG, I'd say it's a no brainer at that price - QF Y is coming in at $2500 for the same time. Plus if you connect to the right flights, you can get the new 777 ex-SIN.
BA PE is better than BA Y
When we last did Y+ on BA, it was the same food as Y.... Didn't see the Y+ menu, but what was on offer for the dinner ex-SIN seemed to be the same meals as Y. Not the same plates or wines tho.
I flew WT + YVR - LHR about 5 years back, and it wasn't that bad. Sure QF Y+ is far superior on the A380 and refitted 744's, but QF Y+ on a packed older 744 isn't that great. There are mixed reviews of the CX Y+ product, and the price is much higher.
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Y+ on refitted 744's has same new seats IFE etc as the A380 and I assume same service, but the overall A 380- experience with airflow, quiet etc would not be there. Nor would the sense of separation from Y, they are just behind you through a curtain.