I've had my 5500 for over 2 years now and my 5600 for nearly 1 year. Loading applications on the 5600 is slower than the 5500 because the 5600 uses slower non-volitile, flash ROM for internal storage, whereas the 5500 uses volitile RAM for internal storage.
Other than that, a 5600 running at 400MHz (either with the fixed CPU or the Special kernel) is faster than a 5500, but of course there are other speed bottlenecks which mean that the 5600 is no where near twice as fast as the 5500.