Originally posted by JinDesu Price-wise, the Canon 70-200 F4 is a good lens to use to compare, as it is pretty much half the price of the F2.8. It's also smaller, and lighter. It would be nice to have more F4 options, but I think we're pretty covered for that.
I'd be interested in top-quality F4 zooms for half price which are smaller and lighter. Take for instance the DA* 16-85mm on the roadmap. If it's f/2.8 I likely can't afford/justify it, plus it might be too bulky to be my general "walking around" lens that I keep on the camera all the time.
But if it's f/4 then I probably CAN get it and use it regularly. It might end up replacing my 18-135mm WR (DA* is weather resistant too) and even though it's shorter I can use the 55-300mm to cover the long end and still have a little bit of overlap between them.
The DA 17-70 is possible, but I really prefer for my everyday lens to be weather resistant if possible. Nor would I really want a 28-70 (or 75 or whatever) no matter how good it way because it loses too much wide angle.