Although I have Solus 4.4 Budgie installed on a Razer 15 laptop, which updated from 4.3, I went ahead and installed Solus 4.4 Mate on a Dell Optiplex 755 Desktop.
Smooth as a hot knife through butter!
No issues at all.
Least I can say tonight that I actually did install 4.4 from ISO.
Chose Mate on this spare machine, so I can follow the eventual process to Xfce out of pure interest.