Just warning. If you want the NCR and the BoS to get along later in the game, side with the current elder. I wish I had.
This makes me sad... I have always had a soft spot for the BoS, and when I found them I had decided to stay with the NCR.
So instead of killing the NCR guy they told me to I informed him, and am now heading to their bunker to finish 'em off for good.
Is there any way to get the NCR guy to leave without a high speach?