I just got back from the woods and from blasting a big pig with that 260 and the 120 grain bullet. The answer to your question about why would I consider going to the 100 grain Ballistic Tip is that I'd like to get above 3000 fps in that 16 1/2 inch barrel and flatten the trajectory just a bit out to 400 yards. But, this afternoon's pig was at 350 yards and with the use of the Burris BC dots, I knocked the pig flat on the spot. So maybe I don't need the 100 grain bullet after all. The Burris dots are dead on at 200 and 300, so maybe I just better leave well enough alone. This coming week, I'll try out some Reloader 17 in the rifle and will try both the 100 and 120 grain bullets. Whichever is more accurate is probably what I'll use. Anyway...that's what I'm saying right now. I might just stay with the 120 grain version.
As for the 220, I think I'll work up some 65 grain Sierra loads and try that on a few pigs just to see if they'll flop over on the spot. I expect that bullet will stabilize, but I haven't tried it yet.