Long Jump

A single big fling covers it. In any chamber where you can place portals on both the floor and a facing wall, drop a portal on the floor and another high on a distant wall, then fall into the floor portal - you'll come flying out of the wall portal and sail across the room. 300 feet is roughly one good fling in a tall room; the wide chambers later in the game (or the fling rooms in the escape) work nicely. Optional stunt.