Hi Brennmat,
Thanks a lot for your input, much appreciated 
So you say that anything under 16mm will likely produce bad results (even if it’s not a fisheye lens but a good ultra wide with minimal distortion)?
As you know a difference in 5-6mm (say Tokina 11mm or Sigma 10mm vs 16mm) can mean more than 20° difference in the angle of view, so ideally I’d like a lens that goes as wide as possible.
Sincerely,
Thomas