Standard UK gauge is 4'8.5", which is indeed the same as the US uses, as does most of Europe
With the advent of more demanding consumers, companies like Peco, produce more prototypical profile track. An OO scale Locomotive will run on code100 track but will ride on the rail ties especially over turnouts if using code 83, as code 83 has a lower height profile as that is more prototypical for a RR.
As I run both HO and OO locomotives, for me, it stands to reason that I use Hornby standard or Peco code 100 track, as the HO will run perfectly well on this scale track. And if I'm honest the height difference is not noticeable at more than 2 feet distance.
OO has a scale ratio of 1.76.2 and HO is 1.87, there is a reason for the differential, and why the UK still uses OO scale and not HO, I've posted this before, but I'll repeat it here. this explains why the UK uses OO scale compared to the rest of the world.
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