I don't recall the stats on Ulthring's set (they are listed in the DKS
FAQ/Guide). Some people like that set, at least partly because it is only 4 pieces, so allows greater flexibility in choice for other equipment.
With my ranger in DKS I used the full Mining Guild set (available in the Steam version and the North American Xbox release) from level 16 to 27, replacing everything when I could use the Bow of Orobas after getting to level 28. I checked out other sets in the game, but (except for the mining Guild set) stuck with my collection of mostly random equipment (after the beginning of the game no random bow came close to the unique ones available). I used the Orobas Bracers (also Steam / NA Xbox) for most of the time I had the Mining Guild set (level 16-25), but without any other pieces of that set equipped there were no extra bonuses.
In the original release of D2:ED I didn't use any sets with my warrior.
Kali is Hermosa's sister, and can be found in the headquarters of her flying fortress, which is in Rivertown Gorge.