I would not pay an additional £600 to fly QR over CX - in J the most important perk for me is a lie flat seat and you'd be getting that with CX. If pampering is what you're after save that money and splurge at your destination.
Having said that if you are willing to pay up to £4600 for your flight you can fly in first class ex-BUD for around that much in Jan/Feb 2024, albeit on Star Alliance. I'd definitely pay £600 extra to upgrade from J to F.