Furthest, I think, is Mayhem 20 (No added colours or lemmings), Away from Fun 4 (A task for miners and climbers).
Closest... Is a bit harder. Running mentally through the levels, I think the answer is some WAFD level. ... I think the two closest are WAFD Taxing (Taxing 30) and WAFD Mayhem (Mayhem... 11?).
That said, I am unsure of the latter (or if you count the WAFD levels in that assessment), so I'ma wait for confirmation of how correct it is before I pose a question.