There is a ten piece equipment set in each of the fortresses for Stone (Archmage set), Raze (Hunter's set) and Kali (Scorpion set). If you mindread those three bosses, as well as Xanlosch (in Stone's fortress), you can collect the four piece Ulthring's set.
I checked out each of the sets when I found them, but didn't make a note of the stats (some of the stats, shown in green, depend on the number of pieces of the set that are equipped). None of them tempted me to switch from the collection of random stuff I was using. A couple people that posted in the Finished Divinity II ? Tell us with which stats
topic used some or all of the sets, though, and at least the archmage set has been recommended as a goal for mages to get. A couple people have mentioned they like Ulthring's set since it is only 4 pieces, and allows for more flexibility in choice for other equipment.