As for "quite good", it's weird. I never think of it as a US phrase. It's sort of a quaint little way to say "very good," and almost has to be said with at least a trace of a british accent to make it work. ("Quaint" and "British" have an oddly large overlap in the US mind, for some reason.
But if you want a 'quaint', British-sounding way to say 'very good', then 'rather good' would be the one to go for.
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Momentarily can be used either to mean "in the very near future" or "for a brief time." It depends on context. Basically, it can be "in just a moment" or "for just a moment." Either works, although the former is more common.
And in UK English the only acceptable meaning is 'for just a moment'.
The more I think about it, the more I realise that I actually have to learn a whole new language having moved to North America!
