ok, that is a loaded question because so much depends on your technique of shooting, and also camera and noise. My D800 has fairly low noise, so,, on this
lens, I tend to set my ISO to 800,, and with fstop of 5.3-8,, the speeds typically is at 1/1000 of a second, which is fine for this lens,
but,, still need to support the lens well, I put on a kirk collar,, which offers a perfect hand grip when not on a tripod,
so,, I tend to brace my elbow to my chest, gripping the Kirk cloar, with my left hand, and then grip the camera/shutter with the right,, and really am
careful not to tilt when pressing the shutter, since any tilting motion will cause a slight blur, with the higher pixel cameras, you have to maintain
really really good form,, but with practice,, the pictures come out razor sharp.
here are a couple hand held shots
first one is at 1/1000 of a second
View attachment 105947
and second one is 1/600th of a second
View attachment 105948
both hand held, and manual mode, shots with this lens.
and here is a recent shot, cropped to 1/4 of the image (because so far away even at 400mm), hand held at 1/320th which
is about as slow as I want to hand hold this lens.
View attachment 105952
not bad for a cropped shot,