If i am not mistaken, the draugr death overlord is the highest non boss enemy you will encounter in ruins. They start spawning at level 47 or so, if my memory serves. And boy do they spawn, facing 3-4 death overloads shouting + wright overlords that spam frost atronachs and what not lol.
The bosses for most ruins, will be changed to dragon priests that will spam expert destruction spells, along with an expert conjured atronach.
With dawnguard, the highest level enemy you will encounter will be legendary dragons, which start spawning at level 78 (according to the wiki).
With Dragonborn, you have the Ebony Warrior at level 80-81
Try NOT to Op you'r self, one of my profiles hit level 102, and i was just 1-2 hit killing everything with dual steel swords dealing 550+ damage each on master....it gets boring really fast (armour cap was reached with 600 armour to be safe, magic resistance was 80% and elemental as well was in the 70% range). Basically, on master, the only thing that actually caused damage to me were ebony arrows from deathlords. everything else....a walk through the park.
But that profile was me "pushing" everything legit, no glitches, no exploits nothing, pure clean gameplay.