I am forever testing lenses. I used to line up a camera with a book case in our old house and test all of the extremes of focal length, aperture and frame area, turning a chore into a bit of an art form. Lately the method has simplified to just taking some snaps of consistent subjects and viewing at normal size on a biggish screen. A waste of a frame really.
Poor Pepper or, as we also call her "Miss Daisy" has been my muse for the last few years since we adopted her from my brother in law. She is very photogenic, patient and has reliable habits as she wanders from room to room following the sun. This day I had the 75-300 in hand and noticed her winding up for a bark at a passing dog. The shot was the usual, aim for the eyes (Olympus eye detect works on dogs!), hold steady and shoot. The result is an image nearly impossible only a few years ago. A hand held 600mm equivalent focal length, indoors in fading light at ISO 400 and a slightly moving subject. The aperture is f6.7 (wide open on that lens and apparently its weakest point...hah!) and the shutter speed was about 1/60-1/125 of a second. IBIS on even the older EM5 is good enough that sometimes you forget old habits and try improbable shots.