[The Might]

Wow, that's a hard one since I can't imagine where to start looking.
Apparently they had little to do with each other, but surely there is something if you say so.

The problem is a lot is said in the books about them and if they are the only ones to have it in common then it must be some minor detail hard to find.

Ummm... maybe the fact they both heard that Hasufel and Arod had met Shadowfax that night near Fangorn Forest?

I know it's a strange answer, but nothing else comes to mind right now.