The Path Tracer uses Defer All for shading, which is why it handles some surfaces better than the normal renderer. You can enable Defer All *separately* from the path tracer and it will be faster than with PT (but with the standard lighting, not a realistic). Defer All should improve surface quality for displaceable objects, including the plant, terrains, etc., but I don't think it should affect non-displaceable objects, for example any imported object.
- Oshyan