I've read all the information available on mesh collider optimisation, but I still can't answer my main question. How much of an impact on performance do STATIC mesh colliders have?
For example, when making an environment for a game (shooter), should I heavily optimize the environment's props collider? Or can I use a props mesh grid for its own collider? This question is especially relevant within a shooter, where the registration of the bullet hitting the objects should match the shape of the environment objects as closely as possible.
I experimented in two major projects as well (Insurgency Sand Storm and Squad), and the hits were registering in absolutely everything, even the smallest details of the environment, creating a strong sense that the colliders exactly match the mesh of the object.
