If you haven't already, check out Ray's site. There are lots of good pictures of his tarp set up different ways. There's also an interesting video of a cuben fiber tear test, which seems to put the lie to the idea that it's stronger than silnylon.

The "variable geometry" idea regarding the beaks confused me at first. In fact, I didn't really get it until I'd made the tarp and set it up. The beak actually becomes a vertical wall if pitched very low and wide.

The square tarp with no beaks could probably be set up more different ways, but it seems like you'd want it a little bigger.
I've only used a square tarp once, and it was 10'x10' and big enough for two people.