The thing with oak in the Upper midwest is even standing dead it doesn't ever dry out. I've cut unto gypsy moth killed red oaks that had been dead for decades. The outer inch or so would be powdery/punky, but past that the center would be nearly as wet as a green tree. As such they are not that hard to cut. Sugar maple on the other hand if it's cut standing dead and it's not rotted(which is rare) is very hard because it drys right out. Elm standing dead is also pretty hard/dry when standing dead, even though it's density doesn't suggest that. Hickory would be another tough one when standing dead.