Since you aren't in a big hurry you might want to keep watching for new lens introductions, five new FF lenses on the
D FA roadmap. I don't have a K-1 or any of the new FF lenses so I can't say much about them. There are some older FF lens that can be had at bargain prices, which you've already found one. The F-35-70 zoom is a good one, as is the older FA-28-105 4-5.6 zoom (or Tamron version (same lens). As for a longer zoom, the d FA 150-450 is supposed to be a beast of a lens, but has a price out of your range. There are probably not any older FF zooms nearly that good, at least that are in your range. Your post made me realize that I would not have many FF lenses to make the jump, but I think I still will eventually, but I'm in no hurry.