The wilderness map marks the Hexes as 5 mile but the text in the Vicinity chapter says they are 6 mile. Which is correct?
Either, truthfully.
The Labyrinth Lord version, I believe, went along with 5 mile hexes, which I think was original to the map (as sourced from OD&D via Outdoor Survival).
In the ACKS version, they were declared as 6 mile hexes, since that's what ACKS' rules default to; and I believe earlier printings/PDFs may have (or still have) some discrepancy.
The important takeway, though, is that it's not a huge difference, and it's completely safe to assume 6 mile hexes when using it with ACKS.
What he said!