390, 430, and 470 are pretty meaningless without useful units, using a scaling ratio of 15:352 we can convert them into miles per hour, a much more meaningful and British unit.
390 = 16.92 mph
430 = 18.32 mph
470 = 20.03 mph
I kept it as 4 s.f. so conversion back to UU was possible and accurate for those that were of such an inclination to do so, although if it were me I’d tweak the actual UU’s to give ensure the mph’s were as close to 0.5 mph unit boundaries as possible.
Minor comment: since the game is international if you include ‘miles per hour’ then there should also be a mention to kilometres and/or metres as well.
If I were playing a game from developers in another country where the game were based in their country I would expect to see their units. This is a British game, by British developers, based in Britain, so I would expect it to use only mph.
I think using game units in development is maybe more useful to the people co-working on same project from different angles, more significant numbers are likely to be available upon release
To be honest I’m not sure what are the units you were referring to in your first post.
If it pertains to the development side of the game it makes sense to be in the units that the developers are familiar with.
If it pertains to the user side it makes sense to have them showing both in imperial AND in metric units.