Some years ago, I heard that a rough metric for regular athletics: humans slow down by about 5% for each doubling of the distance. If that is accurate even between 100m and the mile, then extrapolating the world 100m record (9.58 seconds) out to the mile would suggest a mile pace of 12.84/100m.

Kerr ran an average of 13.837/100m. If the 5% rule is truly accurate (which is unlikely), there's some scope for faster times. Personally I'd bet the 5% is just a handy rule of thumb that doesn't do much more than to indicate that these are incredible athletes operating at the absolute peak of human performance.