Raycast performance - 2 layers + 1 or 2 raycasts ?

I just want to know something about raycast performance.

Lets assume i have 2 layers: enemies and ground. Im performing raycast in update to have continous RaycastHit data whats mouse is pointing at. Sometimes i need to use RaycastHit data for ground, sometimes for both ground and enemies.

So now i need raycast over 2 layers and i want to know if performing one raycast for ground, and second raycast for enemies would be much worse in performance then one raycast for bitmask containing both layers.

Why not using tags, i mean you can check the distance with an infinity ray and you can have one raycast for all you want.
If you don’t know how to do it, tell me.