I received a few positive responses regarding 64-bit, but no one seemed to be using Pro/Engineer files located in a Windchill workspace (although one person reported success while connected to a Pro/Intralink 3.x workspace).
I had a test system set up with * Windows XPx64 * Pro/Engineer Wildfire 4 M140 x64 * Ansys Workbench 11 SP1 x64 * Ansys Workbench 12.1 x64 Pro/Engineer was connected to a Pro/Intralink 9.1 M030 server. The Pro/Engineer files were located in a Windchill workspace.
I had no problems attaching the Pro/Engineer geometry in Workbench or updating the geometry from Workbench after making changes to the Pro/E model.
Now, ready to upgrade one user to 64-bit to see how all of our other software behaves in a 64-bit environment.