Where I live the trees aren't really huge or anything...so the total length of the loop would only need to be like 24 to 36 inches end to end.
But with that said maybe a big loop isn't really the way to go.
So but even still? Whats stronger? Knotted or sewn? If I used a knot it would most likely be a water knot because its pretty clean and easy to do.
Oh and thanks for the great responses so far everybody...keep em comming