According to AY timetible, you will be able fly SYD-SIN-HEL-LHR in the same A330/350 business class :) Finnair use widebodies on the HEL-LHR route, too.

Finnair being creative again, they also have a wet lease agreement with Qatar, Finnair's A330s feed Doha from Helsinki, Stockholm, Copenhagen.

Finnair's entire widebody fleet will get the new config by the end of this year

Oddly enough, Finnair's hub HEL actually is closer to SYD than any other EU hub, even closer than ATH.  The HEL-HKG-SYD routing is very close to the shortest Great Circle path to Europe.

The smaller Business Class cabin can be converted into Economy so there are luggage bins for the middle seats. For the same reason the divider between the smaller Business Cabin and Economy is rather light so I would avoid the last row in Business.