[stoppingdown]

First round of tests done. Procedure: exposure: using zebra; drive mode: single shot, roughly one shot per second; ten shots per each set; pre-focused only once at the beginning.

Subject at roughly 5 m (IS0 100 fixed, changing aperture from ƒ/2.8-9-18 since it's in the shadow), percentages of sharp shots:

1/800: 100%/100% (IBIS on/off)
1/80: 80%/40%
1/20: 70%/0%

Subject at roughly 1000 m (ISO 100 and 50, changing aperture from ƒ/4-11-22 since it's in the sunlight):

1/1250: 100%/100% (IBIS on/off)
1/80: 70%/50%
1/20: 40%/20%

Of course in evaluating sharpness I focused on motion blur, since absolute sharpness varied because of diffraction when stopping down a lot. I'll try to redo the test in more homogeneous conditions, but I think it's enough to prove my IBIS isn't broken. At this point it probably makes sense to refine the test to have a rough estimate of the actual stops gained.