It was a painful process but once I had done it, I ended up liking a slightly expanded version of my 500-word SOP more than the 1000 word one. It said all the same things, with a lot less fuss.
It wouldn't have been so bad if they just wanted the purpose part...but they also wanted the personal part so that made it tricky. I don't really like it, but it's as good as it will get.