I have found some rota boost they 5x100 but off a Subaru are the centre bores the same

No, they are just too small, you need adaptors or get them bored out to the right size.

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what he said ^^^^

 

But...... given they are a third party wheel rather than OEM they may well have a large centre bore to make them more universal and have been using spigot rings to fit the Impreza.

smaller (or bigger dependant on your favoured phrasing) spigot rings and they may bolt straight on the Fabia