I'm 5'5" and I like find that 10 feet is great. I think I got 3.5 yards and whipped the ends. But then again I like a really flat lay to a hammock. My hennessy is shorter than 10 feet (measured around the bottom, not the ridgeline length) and is less comfortable. If you are comfortable with more of a curved shape while you sleep then feel free to go shorter.

Also I prefer using wide material (60") rather than narrow (48"). That also contributes to your ability to lay flat. But other people feel differently.