If you are looking for high elongation at failure - you should look at fibers used in ballistics applications. The name of the game there IS high elongation and energy dissipation.
Carbon and glass are too brittle to work as a continuous pultruded product. You might get there with some kind of discontinuous media.
as far as achieving a modulus of 800 ksi, I imagine that it won't be difficult. Kevlar has a Young's Modulus of 60 to 180 GPa, depending on type. Even a low fiber volume in a composite will give you the 800 ksi you seek.
I could really narrow the field for you if I knew more about the application....