... oh, about 2 or 3 seconds with a 180mm lens... in a candle lit room... with some Norman strobes, rear sync of course.
For real? I try to never shoot handheld below 125th with lenses under 180mm but I'll push that to whatever if I don't have any choice, I use burst mode too. I simply don't try to handhold longer lenses than that... if I'm carrying a long lens, I'm carrying a tripod./
When I was in my 20's, I routinely shot a handheld 300mm f4 in bright daylight and got great results. I've been shooting in service rifle matches off and on throughout my life and definitely apply the same settling and meditative techniques to both photography and match shooting.
Advancing age and digital photography, more specifically the 1.5x lens factor, have humbled me in terms of handholding long shutter speeds... now, I go for camera support and strobes.
Chip