Thanks for the reply, Don!
I see what you mean about the 18-250, but I wont mind carrying two lenses on this trip, and I really want to have the best lens for use after the trip also. I will already be bringing the 70-300, just to be stealthy around the wildlife. If the 17-50 is the better overall replacement lens, it sounds like I might be better off with that one. It is all very overwhelming to a beginner