I don't have stock wires/boots but mine should be close. Stock boots are longer than the NGK's I use. 10 inches per wire should be plenty. That will allow you to clip 'em once in awhile to ensure good electrical connection.
M.M., I'm running straight NGK 5K resistor boots and regular 7 mm automotive copper core wire. I get 4 feet of wire for about $6. Boots are about $4 a piece I believe.