i use the 673 release to upgrade older classic versions all the time, then import to 7.5.8 threads. that readme isn't right.
i'd just go for it ( with a full backup in place as a safety )
for me, i actually just download all files to my local hard drive and run a local WAMP (
http://wampserver.com ). then i run the upgrade locally, so any bugs or errors or {insert scary things that could happen here} occur on my local install.
i then work thru any kinks and upload the new stuff to the actual running website.
