The only reason I can see for Ben killing Locke was that it was the only way for Ben to take control of the situation so that he himself could get back to the island. I doubt he really cares about the fate of any of the losties at all. He may have a fondness for Locke, but this is now the second
time he's going to have killed him (though the first time didn't go so well). All Ben does is manipulate, and I doubt Locke... or anyone else... is nothing but a means to an end for him.
I suspect once Ben wakes up, he'll feed Locke a story involving Sun (it looked to me like that
was the moment he decided to kill Locke, when he realized Locke hadn't spoken to Sun... he just couldn't do it until he got all the necessary info from Locke). As for Widmore, I don't consider him much better than Ben but his story at least made sense given what we know so I'm inclined to trust him for now... at least concerning his backstory.
Uh, anyway, excellent.