After creating the system yesterday, I took the liberty to improve and modify it a bit. I managed to improve the speed, while increasing precision. Alongside that, I've included a debug object that displays all kind of useful information. The engine is running 60 fps all the time, except when moving the nodes of the NavMesh. That is because at this time, the pathfinding grid is being calculated (and displayed) whenever the mesh is changed, which is quite resource costly in GM. In the game this won't happen as the grid will be pre-calculated.
Here is the first video preview of the engine, displaying the NavMesh and the pathfinding.
Turn on the captions!