Hi thank you for your answer,
the NavMesh graph has more advanages. Like, the margin around the collider have a much more better layout (around the unit). So Units are not colliding in the corner of other units. I can optimize now the margin, don't have to make it to large. It solves a lot of trouble around pathfinding, like hanging in the wall beside the door. Also the pathfinding time is much more faster (0 ms ). I need 4 NaveMesh graphs for different sized units and it looks like that won't be a problem.
I will not try to speed up the GridGraph, because I see much more advantages in NavMesh graph. I'm using a xeon E3 1231, kind of I7 47XX, not mobile! And yes, I had for one of the 1000x1000 graphs the grid visible.
However, Recast-Graph is awesome. Nice thing is, that I don't have to change much to replace the graph. I have just to recreate the graph.