Been looking at some 'Audax' bikes and most seem to be steel. Any particular reason for this choice of material over alu?
I'd suggest: tradition, longevity (alu frames were brittle and susceptible to fatigue failure in the early days) and, it is said, greater comfort due to the 'spring' of a good steel frame.
quite a few even dyed-in-the-wool audaxers rocking up on carbon endurance frames these days though... geometry wise there's not a massive amount of difference
I'm still working on the beard in order to become a true audaxer!