MR's come up often enough, and someone will probably jump in and give you his ultimate-mileage AONE3 route, but you might want to just read through a bunch of messages going back in time to get some different ideas. Personally I can't imagine spending USD7000 just for a medium pot of miles, but some people have better uses for them and don't mind.

Just to get you started, LHR-DXB is popular, and you can also do LHR-IST without busting a rule. In NA you probably need to include DFW-ANC.