I work with RW 5.3.2. (5.4.1), RW 6 and RW 7 on an iMac (17" / 2013) with High Sierra without problems.
(Regularly many Web sites)
Version 4 but seems to be very old…
High Sierra has many compatibility issues with older software. A lot of the problems only come to play if you convert to the new file system. If you’ve got an SSD hard drive, you don’t have a choice in converting.
My suggestion is unless you’re going to stay current on your applications, then don’t upgrade your OS.
My understanding is RW 7 is the only version that works entirely with HS, and it’s the single version supported by Realmac.