I wouldn't trust OIDs, because they are 32bits for once.
Secondly, Watch for index size. That's the main reason why (big)int as
a key reference is a win over other types - at least in my general
practice.
And third advice, try different approaches, and queries - to figureout
what would suit the solution. Anyone who says, that this is always
win, and something else is not - is a lier.