There\'s jsut a couple of reasons to get the 5600.
1. If you absolutely MUST have a built in speaker
In my experience, these almost always suck and I do not miss having one on my 5500
2. You are too ingnorant/incompetant/indifferent/lazy etc. to install a custom ROM, because with the default sharp roms, the 5600 is remarkably superior.
With any of the 5500 rom NOT made by sharp, you can combine a memory card and a different memroy split to get double the RAM of the 5600 which can never ahve more than 32MB of RAM for programs.
3. You will be constantly doing highly CPU intensive things like playing divx movies in full qvga resolution.
If this is the case, you will have to be very carefull as most 5600 come with a pxa250 which has a very slow front side bus and is actualy SLOWER than the sa-111 201mhz cpu in the 5500. THat\'s right, I said the 400mhz Xscale is SLOWER than a 201mhz strong arm. CS-101, there\'s more to actual cpu proformance than clock speed.
Some smaller number of the 5600 were produced with a pxa255, which actualy IS faster, so if you need massive processing, be sure that you are getting a 255 and NOT a 250.
THat\'s basicaly it. What IS wortht the extra money, IMNSHO, is an sl-C760 or sl-C860. Then you can use the beautiful cacko pdaXrom.