You have some great cycling there. Gurgle maps puts you just NE of Adelaide. I watch the Tour Down Under every January, not so much for the racing but for the scenery. Marvellous countryside there.
Audax bikes in general make great commuters. One of mine is the Ribble Winter/Audax. Aluminum, but still an audax bike. And true to its name, it loves long rides as well.
There's nothing in the geo specs about the fork or "trail". My comments here are based on audax bikes in general.
I'd drop down a size to keep the stem in the 100 to 120 range. Audax bikes tend to have "low" trail. (See
Trail and Its Effects at Spectrum Cycles.) A short stem is likely to exacerbate its effects on handling and make the bike feel all wonky.
I like the way my low trail audax bike feels in commuting, especially on rough roads and the cobbles. That it wants to keep tracking straight ahead is a real boon on bumpy roads in traffic. But it took some getting used to--especially the cornering--since my other two bikes are high trail and neutral respectively.
Yeah the Tour Down Under was fun to watch this year, the finish line was a few hundred metres from our house. Some of the roads they ride on will take us some time to build the courage to try like Menglers Hill, very steep and curly.
I'm hoping to try the smaller frame on Saturday and see how that goes. They will also change the stem for us to see how that goes too.