Can the Oracle itself be migrating birds?

In making a choice it is important that the preposition describes the relation we intend and the word/phrase to which it is applied.

Brisk pace is a specific speed, and so falls neatly in the ‘at speed’, ‘at slow rate’ etc.

‘with’ implies we are taking it with us, and we could indeed say ‘we move with speed’, so it is arguable to use ‘with a brisk pace’, such as in ‘with a pen and brisk pace’. On its own, though, if we asked why not stop using ‘at’ then we might start asking why not use ‘at’ instead?

‘In’ sounds like many translations, where the translator attempts to bring a specific construction that works well in the source language into English, with the hope that it will still work here.