I've never gone from 6.0 up to 6.5/6, but any of my upgrades to the latest version (usually 6.02/3 to 6.06) have been flawless. My process was this. In Imail, stop all services. Apply patch. Reboot server. No problems as of yet. By the way, these were all done on Win2k servers with or without SP1.
Good luck.
