The crops in the shots are not of the same size, and thats due to the differens in MP of the sensors, 21.1 vs 16 i think? And i had to stop down the Sigma to get ~equal dof. (f1.9 would have been better..)
The sigma appears a tiny bit sharper, and that is stopped down (wideopen its not) and thanks to the bigger sensor. Well thats about as far im prepared to go in to that discussion.
Have a look at the pictures and make up your own mind as what combo you would prefer.
My empression so far? Well, its not going to come of my Om-d for some time i am guessing. I totally love it, i love the 17.5mm aswell.
The 17.5 has somewhat wideangle wich makes it a bit harder to shoot with. but when you get it right, it is right.
When you get it right the same goes for the 42.5. But with the 42.5 you can take a dump right where your standing. Then take a picture of it, and its going to look awesome.
Its not quite that easy with the 17.5 even though its awesome.
(but thats my opinion when it comes to most quality 35&85mm FF equivalent lenses. 35mm looks better but is harder to shoot with, due to the wider angle)
More updates later.