I measured one of mine at 23ft for an 8:1 (tied to a separate traveller line) Perfect for bouy racing - no spare line to get caught on anything. I used a 30ft line for the Tybee - again tied to a separate traveller line - too long (the scissors came out on the GT300).
30 ft overall length is probably about right on an 8.5ft boat with no wings (obviously this varies a bit depending on stack height - but you aim to be pretty close to block:block at max sheet tension).

Chris.