I agree with Rifleman, a 240-250 cast keith style SWC will do quite nicely for a treed bear. With a bear you want penetration first and foremost, especially for a larger animal.
My brother has killed two blackies with a .45LC, 255gr cast RNFP at maybe 850 fps. Both times he grabbed the box of plinking ammo rather than the heavier hunting loads I made for his Ruger. Put em in the right spot and they did the trick.