I earned my QF Gold=Sapphire the old fashioned way (international F). It took 10 days (and less than a month to reach Emerald). But as an academic exercise, someone in Australia commuting SYD-MEL on J fares would earn Emerald after 12 round trips (routing SYD-CBR-MEL) and can renew after 10 round trips in subsequent years. SYD-CBR-MEL is 438 miles, so this is 5000 miles. SYD-MEL is the most heavily traveled route in the world (more passengers than LGA-DCA or SFO-LAX!) so this is a realistic scenario. QF has other (shorter) routes, such as SYD-NTL (103 miles) so it is possible to do NTL-SYD-CBR-MEL which would make Sapphire at 3600 miles and Emerald at under 8000 miles. I'm sure it could be done for less. While on AA it is a minimum of 66,666 miles (flying excusively F fares) or more commonly 100K miles. But much more fun to fly JFK-SYD-HKG-LHR-SFO-BOS-JFK which would also earn Sapphire provided it is flown in F.