Scott,
I'm sure you've likely visited this site before but I'm going to post this link in case you haven't or the benefit of others who haven't. It's a great resource for subsonic 7.62x39mm information.
http://members.shaw.ca/cronhelm/762Page.html
He posts on various web boards as Suputin or Suputin221 over on 300blktalk.com . He's a good guy and is very knowledgable and helpful.