Voyager vs the Cube in part 1 of Unimatrix Zero where they take an absolute pounding even leaking plasma from a Nacelle and the shields are still up + Warp Drive works
Don't forget the USS Defiant in Sacrifice of Angels where the ship takes sustained damage for extended periods of times and the shields remain up. In "What You Leave Behind" (SFX scenes show Breen Torpedo's directly hitting the hull and bypassing the shields meaning they were down) and I don't think they drop any lower than 30% in the dialogue.