Gauge and scale can become complex when looking at model railway with only some countries being represented properly. I am going with N gauge which is 9mm track and for standard gauge (1435 mm) is close to 1:160 (about 1:159.4).
For various reasons including the size of the trains (loading gauge) being smaller and the motors at the time of the establishment of the model scales being too large to fit British trains went off scale and went 1:76 rather than 1:87 in HO and called it OO and in N scale went with 1:148.
Japan, where my first couple of locomotives are from, went with 1:150 for their standard trains which run on narrow gauge (1067mm) and 1:160 for their Shinkansen high speed lines which run on standard gauge. I think they model mainly in 1:150 and just accept the different scale of the bullet trains. However 1:150 does not represent the size of their narrow gauge track. 1:150 comes out at 1350mm which is nowhere close to 1067mm so it isn’t true to scale. TT-9 scale which uses N gauge track (9mm) is far more to scale at 1:120 (works out to 1:118.6). That would be a far more accurate representation but it hasn’t been widely adopted so is one of the many specialist scales.
Australia, which has a limited but gradually improving availability of stock seems to go with 1:160. That works absolutely fine for NSW, NT, SA, WA and the national lines in Victoria but is way off for Queensland & Tasmania (1067mm) and Victoria (2309mm). There are probably some small specialist scales to more accurately represent Australian narrow and broad gauge trains.
I’m not sure how companies deal with off scale but I assume they make the height and length of the locos and rolling stock correct to scale and have the error in the width of the locomotive. Given Victorian trains are over twice as wide as Queensland and Tassie trains I think you would lose that sense of size and proportion.
I briefly considered OO9 which is 1:76 on 9mm track (there is an equivalent for HO on 9mm track) but the range is limited and expensive and it represents really narrow track 684mm which is mainly old slate, coal or similar industrial lines and with the exception of heritage lines would mean modelling for not much later than 1930s.
I think my choice will be between 1:148 and 1:150. For me I think most things would not be overly dissonant at those differences (1-1.5% difference) whereas putting 1:148 or 1:150 against 1:160 might be (8-9%). For someone 170cm tall (about 5’7″) it would be 11.5mm at 1:148, 11.3mm at 1:150 and 10.6mm at 1:160 and for a building or structure 5m tall it would be 33.8, 33.3 & 31.3.
As can be seen from this mock-up there is minimal visual difference between 1:148 and 1:150 but a fairly obvious difference to 1:160. So I think that confirms that within the one layout I am happy to mix 1:148 and 1:150 but not 1:160. So no Australian trains for me (or American but I’m not overly interested in American models).