As the range is short and the impact velocity high, I would personally opt for a mono-metal, the weight of which isn't particularly critical. To keep things in context, you aren't shooting at a 1000 pound bear, you're shooting at the center of a 100 pound head, so even a 150 gr bullet at 2550 from a carbine length .308 barrel will be pretty destructive, should you need to lobotomize a bear. The loads I made up for my wife's 21" Husky '06 are topped with 180 gr TSXs, where my faster twist Brno does well with the long 240 gr Woodleighs. With a short barrel .308, it might be tough to make 2000 fps with a 240. I keep referring to short barrels because rightly or wrongly, a dedicated defensive rifle will probably be chosen with portability rather than shootability in mind, and .308s with 16" tubes seem to be in vogue at the moment.