Here's a first effort from the big Sigma 150-500 (only at 190 in this case). Yesterday the conditions weren't all that conducive to photography, as it was windy, and lots of passing cloud, but I did manage this.
At 500mm it's not particularly sharp, as I expected from reviews, but adequate to identify birds. I was actually really surprised how good centre sharpness is in the middle of the range. Pixel peeping this image full size on screen, I could easily count every fibre on the faces lambs if I'd really wanted to take the time.
My previous longest lens was the Sigma 70-300 APO which could just manage birds if I was patient, but wasn't super sharp at 300mm.
Based on first impressions, the 150-500 probably isn't as sharp at 500mm as 70-300 at 300mm, but it looks as though it will be pretty good up to probably around 450mm.
Although the DF-A 150-450 looks like a much superior lens in all respects, it also comes with a much steeper price tag, so I'll have to be content with this.