Agree 100%with what Rob @Rovertek said. If you do make the plunge the license will work all the way to RW8, so I would stop at RW7 until 8 gets a bit more stable. The upgrade from 7 to 8 is a piece of cake.
Upgrading from 5 to 7 is much more involved, check out this help article:
https://help.realmacsoftware.com/rapidweaver-7/upgrading-from-rapidweaver-5-or-6