Wow, what a level! I was going to post a message on theis one but a reply will have to do. I played this for hours this afternoon but have failed to get close to the top few scores. I have a method that gets a few ticks under yours but loses a gem (and could possibly be made faster). Without the gem loss this method is crap. Still, there are a few good ways to start (slight variations) along with some poorer ones.
I don't know how you get 999, but with the scope for choice I would say 1000 is possible... just who will find it first