I believe it largely depends on shot placement. I have seen plenty of buff dropped with rifles as light as a .243 with a behind the ear shot, which is how both of the guys i know that raise buffalo prefer to do it, and have seen several shot for slaughter with a .22 mag in the "magic X" from eye to ear at point blank.
Personally, with your rifle i would think any of the three bullets would give excelent results for lung shots, and you likely couldn't tell the difference in results with a behind the ear shot. My choices would go Berger, Nosler, Barnes, but that reflects my personal ranking of the bullets as well. Good luck on your upcoming hunt!
I think anyone that has used the 300 Berger on elk would have no problem telling you to go with the Big Berger. But since I have never taken a Buff I just don't feel I should pick you bullet. But I thought I was going to go on a Buff hunt last year and I was all ready to take my 338 Lapua and a 300 Berger OTM. I have confidence in the bullet and I had shot enough of them to feel I could place it well.