No Speed for Jib?

There is this awsome rail ledge thing at my school that i wanna hit pretty bad, but the area around it is completely flat. I was wondering how fast (and what method to use) you would need to go to clear it. the gap is about 17 feet. and the ledge is about 8 feet high. i was thinking a jump about 5 feet tall? there is a model i made on sketch up loaded. a href="http://sketchup.google.com/3dwarehouse/details?mid=15a412319afd0ec049ed18fe85d9ed8c" rel="nofollow"http://sketchup.google.com/3dwarehouse/d…/a thats the link.