I obtained the Pentax K-1 because it is FF and works with all of my standard and auto focus lenses.
The camera supports auto exposure and shake reduction with every lens dating back to 1975 when Pentax converted over to bayonet mount.

Test Conditions:
Hand held with SR on.
focus = 5 feet.
Shooting method RAW.
ISO: 100-208800.
in camera NR on AUTO except where noted that it was turned off.
(I saw no difference at 25600 and up so I stopped there.)
Shutter: 1.3 sec to 1/1600 sec.
Aperture: f/8.
Lens: Pentax P-FA* 85mm f/1.4 IF.
out of camera; no manipulation.
cropped to 4 meg (6x4 240).

Verdict:
Pentax claim of 5 stop shake reduction about right.
Noise resembles film grain, not choppy pixelation.
Color cast stabilizes at 25600, close at 51200.
above 51200 only OK for law enforcement or special effects.
Overall amazing technology!