Edit: We added a fast path that covers exactly these kinds of things. Same code, "little" bit different FPS (it's capped at 1000):
Edit2: Added another fast path. 1 million grass entities, my CPU is bored as fuck... GPU on the other hand is currently crying about the fragment operations.
(to be fair, the screenshot is NOT staged, but the FPS changes quite heavily depending on how good it is with keeping up with all the fragments. But then again, I'm on a shitty HD 6770M, so with an actual GPU this isn't impossible to achieve in a stable way)