I've had the lens since the recent sales. I am using it in the Single In December Challenge so if it helps you can follow any progress here:
Single in December 2016 | Flickr
If you like!
General thoughts so far are (yes, some are obvious):
1. It will make for a much more compact travel kit than the FA80-320 or the 60-250
2. The autofocus is excellent; I cannot compare it to the older versions of the 55-300 but it is far superior to the 80-320.
3. Very pleased with the image quality so far - not much to do in post other than the standard tweaks for RAW files.
4. Seems reasonably sharp at most focal lengths but softens up a bit at the long end.
5. Extremely pleased with the bokeh it produces.
6. The max aperture; been a struggle sometimes but then it is December and the days are short and I'm fitting my images around work.
7. I have been unable to test so far with BIF, possibly today but......
8. Feels quite weighty on the K3 but balances nicely and easy to handhold.
9. The quality seems excellent; stiff zoom ring but easy to turn at the same time, doubt there will be any zoom creep
10. Plays well with a Raynox 150 and also my 55mm circular polariser - this means it will pair up with the 20-40 very nicely.
This is obviously a work in progress but its my two penn'orth so far