BA, on the A380 and then changing in HKG? Can be done ex-LHR for £659 on the right dates, though I'm not sure if the CX legs will earn anything. The A380 is probably my favourite BA economy product. As a Gold you're talking about 18k miles vs. 3,500 so even if that leaves you funding the difference, you get most of it back in mileage.
Or an £800ish WTP LUX-KUL and a second ticket on MH? If the LUX timings don't work, MRS or BRU are also quite cheap.