The actual experience of Audax is defined by your speed. That determines the segment of the field that you will meet. So I viewed Audax as an activity for middle-aged 'fitness' cyclists, who use the recurrent challenges as a mechanism for providing base conditioning and weight control. I'd also meet runners whose injuries had brought them to cycling.
It's rare of me to agree with Damian but for once I do.
I'm fast enough to be fast, but slow enough not to a winning road racer.
So, fast audaxing is competitive enough to keep me engaged, but not competitive enough that I have to deal with losing.