Lovely trifid Martin! I saw an equation once to work out what the equivalent integration time would be between different Bortle skies: n hours / 2.51^(sqm2 - sqm1). So if Bortle 7/8 Sydney SQM is ~18.5 and your Bortle 3 dark site SQM is ~21.5, then 2 hours at your dark site would be equivalent to 31.6 hours of Sydney data
CS
Mat