Just playtested Vikings on Monarch to see if harder UHV conditions were possible. Built Vinland AND Shrine of Uppsala by around 900AD (built Reykjavik with one of the starting settlers, hooked up the amber when Roskilde expanded). The territory UHV was easy, although I got it in 1059 I could have done it earlier, just I wanted to play it safe and not give France a chance to take it back before I won. I ended up getting 58 Viking Points, although had I pillaged improvements or sank ships, I could have easily gotten 20 or so more. All the same, I think 60 is the most balanced yet challenging number. Stability was my biggest issue, but that was because I expanded fast at the beginning and lost stability when I razed cities. I think that as the Norse were a civilization of raiders, this should not affect their stability. Here are my suggestions for the UHV:
UHV 1: Build Vinland and the Shrine of Uppsala by 1009 AD (easily doable as long as you build Reykjavik early, get the amber, and remember to build your pagan shrines before getting monasticism).
UHV 2: current required provinces + Skaneland, Norway, and Brandenburg (forces you to build important historical cities like Lund and Stavanger, and conquer Lubeck, which was also important to Viking history).
UHV 3: 60 VP (for reasons stated above).