I have the DO II. Excellent optic, it's perfect for hand holding and loses very little IQ when using extenders to get out to 800mm. For my style of photography, which is more mobile walk-around, versus setting up on a tripod and waiting, I think the 400 DO II is at the precipice of what is comfortably hand holdable. But I'm still curious...
Those of you with the 500 f/4 II: basically, is it hand holdable for regular use? Or, is that the exception, i.e. If need be you can go off tripod, but it'll wear you out after a while?
As with anything bird, more reach + wider aperture = better, but again, not at the expense of mobility. Someday I may be at the point where I settle down and Wimberly tripod it up, but not now.
I've also seen others with the 500 contemplating the DO II. Discuss!!!