.. who holds the record in what time ..
Bringing this back to the original question, it seems from chatter
here and elsewhere on YACF, that it's said Nik Gardner rode the 2018 BCM in 23:40, on a Surly Cross Check single-speed, geared at ~70 gear inches.
So it seems the first step for any aspiring "record" challengers is to get a heavy steel bike with no gears
As has already been pointed out, talk of a "record" in an audax context doesn't really make sense, and for the BCM it is doubly nonsensical as the course has changed over the years, being notably over-distance in the pre-Tout era, for example.