IIRC the 767 used on the ATH runs has the standard Club Europe setup as the IST 767s. Not uncomfortable, but not all that grand. But of course IST is very interesting; one can see a lot in a day, and LHR-DXB-LHR-IST-LHR is a valid route.

I was also thinking you could go LHR-PVG (first class sold on that BA flight) then (your own dime) PVG-PEK on CA - $196 in J or $225 in F one way on a 744 - then PEK-HKG-NRT-HKG-SIN-SYD to maximize FC possibilities on CX and QF/BA.

I don't believe you can transit Asia between Oz and N. America (only Europe-Oz) so you'd need to ride QF metal across the Pacific. If you wanted one last shot at CX F, though, you could go SYD-(SFO)-YVR on QF, then CX888 YVR-JFK, maybe after decompressing for a day or two in Vancouver. The YVR-JFK flight would be your one allowed N. America transcon, but that would only be available if you didn't start the RTW with MCO-LAX. If you started MIA-LHR you could do it, or even MCO-ORD-LHR. (Or, maybe less convenient but you get BA FC, go MIA-YYZ-LHR to start.)

From NYC you could go home with a few coupons left (but only one stopover if you spend a night in YVR or NYC, etc.)