What Kiwi Flyer said, plus if all you are going to do in SYD is a turnround is it really worth the extra continent cost just for those miles?

ARN-LHR-SYD-NRT-DPS-NRT-CGK-HKG-NRT-ORD-MIA-DFW-MIA-LAX-LHR-ARN is 49505 miles. You could easily get more than that with a DONE3 which would be SEK5850 cheaper, plus you could avoid the US$400 charge for the fifth segment in Asia.

Off the top of my head, for example, ARN-LHR-SIN-NRT-DPS-NRT-CGK-HKG-JFK-SJU-LAX-DFW-SFO-LHR-MCT-LHR-ARN is 52876 miles. I'm sure that could be fine-tuned more, and you can get a load more in summer if you go to ANC.