Similar route, only I was from 8700g->Wing->8525->8320. 8700's kb is somewhat larger and easier to type, but I don't do a lot of typing on BB and Curve's kb is much better than Window Mobile. The smaller size easily makes up the difference in kb. I will not go back to my 8700.
Meanwhile, my wife is using the 8700 and she thinks that's the best phone she ever used. Curve is too smoothy/curvy/slippery for her