Obviously there is a lot to see and do in Iceland, so if I do not get an aurora picture, not all will be lost. Looking specifically at aurora photography, I will be dealing with a near full moon for most of the trip (March 18-23) and long term aurora forecasts are not predicting a great amount of activity. I could have picked a better week for the moon as I hear 1/4 moon is ideal (some light on foreground while not blowing out the aurora). But I did target March vs other times we were thinking about to give us a chance.
So, I am leaning toward renting the Sigma 14 f/1.8 Art for a second time. Looking at ebay, I could pick up a Sigma 20 f/1.4 for ~$500 (guessing that is where the bids will end up), and there is a Zeiss 25 f/2 on B&H for ~$700. I am also kicking around the idea of the Sigma 12-24 f/2.8 Art, which would be a rental.
But, out of those lenses, the Sigma 14 f/1.8 seems like the best fit. Especially with the moon, f/2.8 would likely work, but with f/1.8 I should be able to play with shutter or decrease ISO.
Let me know if there are any other thoughts. I'll likely place my order in the next day or so.
Thanks for the suggestions!