Heathrow is a mess lol, seems that facilities are old while LGW facilities have been refurbished. With such a cost difference, I would take LGW-DXB-HKG as a complete no brainer; take EK12 LGW-DXB on an A380 (no brainer). EK380 DXB-HKG gives you a 3hr layover in DXB and you get an A380 as long as you don't book a Monday or Tuesday flight, as those are operated by 777's.