I haven't shot any 140s out of my .260. I have shot a bunch out of a 6.5x57 I once owned. The rifle, a commercial Mauser, was much to valuable to keep.
I took it to the NWTs twice to hunt with a couple I went to High School with. I took a couple of big bull 'bou with it. using 140s at about 2600 fps. Having gained confidence that the cartridge would handle game in the 600 to 800 pound range, I accompanied a fellow worker to his Uncle's ranch in New Mexico and managed to score 5 meat elk in as many trips. I see no reason the .260 wouldn't be capable of the same performance. I haven't been much interested in bear hunting having been turned off while skinning the only one I ever shot. The carcass looked too human for my tastes. I do good work with the 129 Hornady, on deer and hogs. I'm positive it would work if I had to defend against a black bear, which I never expect to have occasion to do.
The .260 is the equal, within a 100 fps, of any 6.5 not designated a magnum, with any bullet weight. Neither of mine have the 9 inch twist, but I know of no reason it wouldn't stabilize a 140 grain flat based bullet. :wink: