There weren't many that could match the high Circles for raw power. Her Blood Warders were butch, but none of them were Masters. The highest Circle character I know of (back in the day) was Garlthik One-Eye, 100+ year old ork ruler of Kratas and 15th Circle Thief adept.
In today's time, Harlequin and Ehran the Scribe are both roughly 15th Circle Wizard and Warrior adepts. You're right, much of their power is still locked away due to the low mana levels, but their connections and skill have few peers (dragons and other IE's can match them, but few others can).