The pennant length is important. It plays a part in the overall scope and it also provides shock absorption. Believe it or not, even heavy chain is not a very good shock absorber. A short pennnat will not be a good shock absorber either but a long one will. If you look at some of the more exposed mooring fields around, you will often see very long pennants for this very reason. Ideally, 15' should be treated as a bare minimum and 20' is much better for your sized boat. Just make sure that you don't hit any other boats because of having them too long.
There seems to be plenty of swing room so I'm planning on going to an over sized pennant. Thanks for the info.