i can't say specifically about flexi as i do not use it. However we are in the process of upgrading to windows 8 at this moment.
I was told that corel x4 may have issues, that graphtec doesn't have a driver that is compatible, that mimaki has a fix but many are having issues, etc etc etc.
i had to buy a new computer, and ended up with windows 8, yesterday i got everything up and running on windows 8, all the equipment works, and decided to upgraded every computer in the building after the success of it.
The price of windows 8 will jump drastically at the end of the month too, by what i understand and talking to a computer tech that also did the beta test of windows 8, most software will work without issue at all, it is drivers that can be an issue, something to do with the "XPS" system and getting away from a "driver" world, blah blah blah.....most of it sounded like charlie browns mom talking to me........