I too was debating whether or not to use mechanicals for Moose and eventually decided to go with a " cut on contact" fixed head. You probably have enough KE to use some mechanicals BUT you are better off with a fixed head.
This link may be of interest...#3 P&Y Moose taken with a Spitfire Mechanical.
http://www.newarchery.com/TrophyGall...&Trophy_ID=234
http://www.newarchery.com/TrophyGall...s.asp?Animal=6