Gildarts is a mountain buster... I don't think any on panel feat of NNT matches that. Gildarts wins.
they do have mountain level feats on panel, just not too many. this is Diane using her Sacred Treasure to lift a mountain into the air and smash a Holy Knight with it.
Dreyfus should be above Diane too by the way.
Is that what she was trying to do? Smash a knight with a mountain? That just made sense to me now. I always thought she tried to smash Helbram with her hammer and the mountain rising was just a side effect.
I remember Dreyfus matching Meliodas blow for blow very effectively; Meliodas, at least based on what i have seen, should be faster than Gildartz. Dreyfus does not necessarily require mountain busting strength to beat Gildartz. He has a sword. And then their is his demon side.