I did some reading on the TH600. It had a lot of good reviews. Like you said, the leak might be a problem. I need a bit better noise isolation. Alpha dog might be in the same tier as TH600. I also read about the Signature Pro. Only if I could audition them all at a local store. Are the Alpha Dog really that great? 6 Weeks is a long wait.
I don't know about the Alpha Dogs but I'm planning on upgrading my mad dogs to them when I can and that is an even longer wait. Meanwhile I'll slum it with my TH600s as my primary closed can. I used it on a train full of people the other day with bass heavy trance music on pretty loud and didn't get any stares so I think it's leaks but not enough to be an issue in the situation.