Prem Econ def.
Done LAX-LHR in Premium on 340 against BKK-SYD-BKK-LHR in WT+ (1st sector was in Club so no valid comparison except crew were quite surly!).
Definitely Premium - much comfier seats and better IFE as there was no reflective glare no matter what angle seat was at. Also the window seat was close enough to the sidewall to lean against it if required. In WT+ (on a 74 anyway) the gap is too big to lean over and rest against the side wall.
WT+ does have it's own separate curtained off cabin but at 2-4-2 on the main deck still just looks like charter to me!!
So much so that upcoming UVF hols in Oct (yeah, might be windy!) are Premium O/B and Upper I/B. Just a shame there's no bar or FBT on the route.