Logic has been doing the same crash thing to me as well. I am running only 64 bit plugs, maybe too many of them but the 32bit bridge is not on. I can not find a pattern for the culprit. First Omnisphere, then BFD then Komplete is listed in the crash log. In a 4 hour session, I can expect 1-6 shutdown/restarts. The latest trick is my permissions for different files change on their own and it's locked as well. I was working on a song for an hour and when I hit save, I got a dialog saying "The location song Song 07 can not be determined" - my DATA drive had unmounted. Oh joy.
Obviously I have no answers but the 32 or 64 question is not what is messing up my Mac Pro.