I hope this has been resolved the vCenter 5.1 Update 1, which was just released:
https://www.vmware.com/support/vsphere5/doc/vsphere-vcenter-server-51u1-release-notes.html
The release notes only mention:
vSphere 5.1 Web Client advanced performance charts are slow to display
In the vCenter 5.1 web client, the advanced performance charts takes several minutes to load.