For those who wonder about SR and focal length
check the forums for posts by me using a 500 mm lens at 1/40. It is with a k7 not kx but SR effectivity is all about technique
edit note. see the photo, not KX but K7, at 1/40 with a 300F4 and 1.7x TC for 510mm effective focal lenght.
considering the "rule of thumb" should be 1/750th for this focal length on an ASP-C sensor, I would have to say SR does do something. This shot was free standing, with nothing to lean on, no rest for the camera, but one hand on the camera, the other at the extreme of the lens, legs apart and staggered front to back, and arms tight in at my side.
this is a 100% crop, i.e. pixel to pixel crop out of a larger image to show detail
there is no way, SR can claim all of the 4 stops here, part technique part SR.