Like chasbmw says, transmissions are risky places to lighten.
Weight savings is always about the sum of little bits (bites?), but in some places reliability and maintenance aren't good tradeoffs. I would want to talk to a rear end specialist prior to removing any metal.
There's weight to be saved in the hub, I think.
"It's not that I don't like people...I just find I am happier when they're not around"