I see my site's been linked again, hope it was helpful to everybody!
Summit is DEFINITELY something you need to decide once you're at the park. There are many many people that get there and then realize how high that slide actually is. Personally, I love Summit, it's a lot of fun.
Here's the specs though. 120ft. tall, 364ft long, it's built at a 70degree angle, you slide at 60mph and it takes about 4 seconds. Yes, you can hear people sliding down it, it the friction between your body and the thin layer of water on the slide itself.
There is also a 48in height requirement to ride. And there's always the chance you may get to the top and realize that you don't want to ride down. You can see ALL of disney property from Summit, even Magic Kindom.
anyway, hope you have a great trip