I recently purchased the DA 560 just in time for my trip to Denali and decided to bring both the 560 and my F* 250-600 (here's my thread about getting the 250-600:
Acquiring the F* 250-600 (LOTS of Photos) - PentaxForums.com). Both lenses performed exceptionally, but they are quite different. The 560 focuses quickly and hunts less than the 250-600, but I also had the 560 limiter switch set to on. The 250-600 does not have a limit switch. The 560 locked focus quickly and accurately. I prefer primes, but the zoom range of the 250-600 is hard to beat.
This is my K10D mounted to the 560. I didn't have my K-1 when I took this photo so I used my Nikon D4 and 24-70 f/2.8G. If you're bored you can read my thread comparing the K10D and the K-1 here:
Ks, 1s, and 0s - My Journey from the K1000 to the K10D to the K-1 (Lots of Photos) - PentaxForums.com.
This was taken in Denali National Park with the 560 on a tripod with the K-1 ii. 1/500, f/6.3, ISO 200
The photo above is edited. Below I'll post the unedited photo to compare unedited photos from the 250-600.
I bought the 560 used, knowing the barrel had a slight wobble. There are some screws loose in one of the sections of the lens and a camera shop is repairing the lens now. I quite like the LensCoat and the B+W Pro 112mm filter included with the sale.
NOTE: I unscrewed the 112mm filter from the 560 and it fit to the front of my F* 250-600. There has been a lot of discussion about whether the F* lens allows filters or not. It does. The threads are not the typical filter size (which may confuse some), but the 112mm filter isn't quite a typical size either. There has also been some discussion on whether the Pentax PF 112mm filter is part of the optical formula on the F* lens. Mine didn't come with one, so I ordered it from Japan yesterday. Once it arrives I'll let you know if it improves performance of the lens.
DA 560 on the left, F* 250-600 on the right, both lens hoods collapsed.
The 250-600 is a large lens. It's heavy too. Although I have taken several pictures hand-held with it, I wouldn't recommend this.
Hand-held image taken with the K10D and F* 250-600. 250mm, 1/100, f/5.6, ISO 100
Unedited and hand-held image from the K-1 ii and F* 250-600 in the rain. 320mm, 1/320, f/6.3, ISO 400
The 560 is longer than the 250-600, but about half the weight, making it easily hand-holdable compared to the much heavier lens. Although the weight is manageable, it's length makes it awkward to hold.
Both lenses on tripods with hoods collapsed. Below the image has the built-in hoods expanded.
I have read complaints online about the tripod foot on the 560 being too far forward. It's nicely balanced with my K10D, but the heavier K-1 makes it imbalanced. To fix this I bought a 200mm quick release plate and attached the rear of it to the tripod.
I have been using a Wimberley Gimbal head with the Wimberley P-40 (about 145mm long) plate for the 250-600. This head was too big to pack to Alaska with my 560 and 250-600, plus my tripod, camera bag, and many other lenses. I purchased a Vanguard Alta BH-250 head rated for 44 pounds of gear on it. This supported the 560 perfectly and worked quite well with the 250-600 at a much more compact size. I did have to crank the knob pretty tight (harder than I would have liked for a head claiming to support 44 pounds) to stabilize the 250-600 though. The Alta BH-300 lists a 66 pound capacity, but this head would not have fit in my tripod bag.
I still think the K10D is the best DSLR ever made.
Vanguard Alta BH-250
In use I thought the 560 was a little sharper. This could be due the heavier 250-600 and possible vibrations due to the weight, or it could be due to it not having a 112mm Pentax PF filter, as mentioned above. Once it arrives I'll take some additional photos to see if sharpness improves. The 250-600 creates incredible images and doesn't suffer from a lack of sharpness, I just found the 560 to be a bit sharper. This could also be due to HD coatings on the much newer lens. When photographing wildlife I found myself reaching for the 560 much more often than the 250-600 during the last two weeks in Alaska.
Unedited image from the K-1 ii and 560 around 4 p.m. 1/500, f/6.3, ISO 200
Unedited image from the K-1 ii and 250-600 around 6:30 p.m. The light was changing quite a bit during the different times so it's not an exact comparison. 600mm, 1/320, f/5.6, ISO 200
Unedited image from the K-1 ii and 250-600 around 6:30 p.m. 600mm, 1/320, f/5.6, ISO 200
The photos below were taken on a different day. It was sunny and harsh light was coming from the sun. I thought the 560 with HD coatings would do better with purple fringing, but many lenses would struggle with the high contrast. The 250-600 didn't show any purple fringing.
K-1 ii and 560. 1/200, f/5.6, ISO 100
100% crop from 560
K-1 ii and 250-600. 600mm, 1/200, f/5.6, ISO 100
100% crop from 250-600