Is the reasonable quality and nice zoom range worth the trade off for slow aperture and dust sucking capacity while zooming? Every use one I considered has dust on the inside so the lens is not all that well sealed so this is a concern for me. And the the slow aperture means low light shooting could be problematic even w/ VR if subject moves. What are your experiences? Am I think through this too much?
Only YOU can determine if you can live with the trade off.
As for being slow.
Until we have a camera with GOOD HIGH ISO (25600+) performance . . .
A f/5.6 zoom is really a day-time lens. Not a night time/low light lens.
I shoot night high school field games. I would love to be able to shoot a light f/5.6 zoom. But then I would be up at ISO 25600.
Old sayings, "
In LOW light, FAST glass wins." And "
you have to pay to play."
If you are shooting moving subjects in low light, your only option is the big, heavy, expensive 70-200/2.8, 300/2.8, and 400/2.8.
So, how much do you shoot in low light? And is that a critical part of your shooting?
IOW, is it worth the cost (size, weight and $$$$) to get the faster speed? You have to make that decision.
As for dust sucking. ALL extending zooms suck air to extend. If they did not suck air, the vacuum created would prevent the lens from extending much, if at all. Many high end zooms have been and are moving to extending design, to store in a smaller space, and advertise as being small.
The Nikon 24-120, 80-400 and 200-500, the Canon 70-200/2.8 R, and the Olympus 12-40/2.8 and 12-100/4 lenses are higher end extending zooms.