With the glass i remember a thread back in the day from Rollercoaster Tycoon 3. Some guy made a test with Custom scenery objects where he put a specific amount of cubers with a diffuse material and the same amount of cubes but with a glass material (same applies to Materials like fliage where the use an alpha mask). The FPS tanked only with the glass or transparency textures / materials. So the glass shader pipeline is still far from optimised and probably as old as the engine back in RCT3 days.