As a general rule of thumb, anybody who has something around an 8 in any rating is bad news. If you're a 10+ you're more than likely on someone's hitlist or they're probably watching you closely. Anything higher than that is bordering on extinction-level stuff. 

The numbers aren't about how powerful you are, but how much of a threat you are. Strangers are about hiding, so they're probably not gonna be able to level buildings with their stranger powers. How hard they are to deal with, etc. If that helps anything.