There should be some clarity added to this warning:
"If you run the upgrade from a remote system connected to the ESM system, have X-Windows running on your remote system. Use ssh -X to run the upgrade."
On a remote Unix system with a full graphical environment this should work fine, but if you are planning this upgrade remotely using Windows, you must be running a local X server, and forwarding your sessions. There are several tools to help, but recommend any all-in-one SSH client and X server, such as MobaXTerm. (MobaXterm free Xserver and tabbed SSH client for Windows) The other popular alternative is XMing and PuTTY.
Make sure to test by typing "xterm" or "xeyes" once your connected, (hopefully one or the other is installed.) If you get a newly created window, then it is working.
According to anecdotes I've heard, the console only/text based upgrade will NOT work. This is in stark contradiction to the fact that a fresh 6.5SP1 install fails if X forwarding IS enabled.