Are the claims that you can use the new barnes triple X true that you can use a lower weight bullet than normal and still get the same penetration?
Yes. Sometimes you can get better penetration from a lighter weight Barnes than you can a heavier lead bullet.
The 270WSM will do an excelent job on elk and black bears.
Since you are self imposing a 300-ish yard limit my first choice would be the 150 grain tipped trophy bonded bear claw. My second choice would be the 130 grain Barnes. Then the accubond then the partition.