I suppose that my question is… why not just use Panda’s built-in “Plane” class, which has notionally infinite extent, and thus not worry about reparenting an object to the player?
(See this thread for more)
However, to answer your question, I would expect what you describe to be very fast indeed!
Just note that, whether with a plane of your own or Panda’s “Plane” class, you’ll only be getting a flat surface–it wouldn’t take into account your heightmap, or any other things that may affect the height at which the player might expect to click. If that’s as intended, then well and good however!