I guess I haven't posted my examples in this thread. There's no reason to use the lens in "crop mode."
IMHO the DA 55-300 PLM is fine for the K-1, as long as you plan to corp. If you think you need every pixel of 36 MP then avoid it. But if a 30 MP crop is good enough......
I've posted this so many times I just assumed I'd posted it here.
The amount of resolution increase from a K-5 will be rather acute even with APS-c lenses. My DA 55-300 gave me cropped 24 MP field that would have been 11 MP on a K-5.
DA 55-300 on K-1
Still a 26 MP file, even better than I could do with a k-3.Twice the resolution of a K-5 file, even using a crop lens.
If you shoot in FF mode and do the cropping yourself, many APS-c lenses will still give you much better than APs-c performance.
In this case, using the same crop I would have used anyway, twice as much.
I did a 19 day canoe trip with nothing but the DFA 28-105, and DA 55-300 PLM... the 28-105 covers most of the focal lengths where the DA 55-300 PLM vignettes badly.
Note: Cropping to 16:9 I can crop to both edges of the frame and get a 30 MP file, that would be absolutely no different using an "FF" lens. But then I crop most of my work to 16:9. I have a DA*60-250, DA*200, Tamron 300 SP AF 2.8, and F 70-210, and I chose the DA 55-300 for my trip, because it performs well enough to ignore its deficiencies as an FF lens.
But hey, that's just me. If you want to carry a 2 pound lens for casual "I probably won't need it use" then go for it.