As many have said in other threads, it won't harm it to leave it on the yeast cake--age will do this one some good. I'd let it go 6 weeks if it were my beer. Than bottle it, tuck it away in a closet, and forget about it for a few months. When you remember it, it'll taste amazing!
Unless, of course, you need to free up your primary. But that would provoke the question, why do you only have one primary?