My son (working in the UK) is allowed to fly premium economy by his employer. If the J fare (on any airline) is less than 10% more than premium economy on BA, he can fly J. He seldom has to fly WT+: EK J or QR J is often within the rules for him.
From CPT, EK J is also similar in cost to BA WT+ (which we flew once). No brainer, unless the time factor is critical (for me, flying via DXB is a 5 hour time penalty vs a direct CPT/LHR flight, but it is immaterial to me)

So my advice is to look at EK J fares and see how they compare to Premium economy on your routing.