This is the most important distinction from 32-bit.
. While 32-bit systems were limited to roughly 3 GB of addressable memory, the 64-bit version of AutoCAD 2011 could utilize significantly more RAM, which was essential for: Large-Scale Projects : Handling complex architectural models and massive Point Clouds containing up to two billion points Autodesk AutoCAD 2011 -64-bit-
Autodesk no longer sells or supports AutoCAD 2011. You cannot download it from Autodesk.com unless you have a legacy subscription contract. This is the most important distinction from 32-bit