I'd describe 'perfect English' as English without any errors.

English speakers are remarkably tolerant of differences in style, vocabulary etc brought about by geography, to the point where they are completely irrelevant to any discussion of 'perfect English'.

I do not hear "errors" when I listen to someone from New Zealand, or Canada, or any other English speaking country, I hear differences in style, and I am certain it is the same for them when listening to me. That is a world away from the sort of mistakes foreigners make which jump out of the air like the sound of nails on a blackboard.