No substitute for lots of long carbide ice picks if your racing on hardpack/ice in front of your favorite watering hole. If your racing 1/4 mile or something and you get them 4-5 lengths in 660, it will take allot for them to run you down. Like Knapper says, a well set up 600 can kill allot of high-horsepower sleds in a short distance. If you have a 3-4 length 660 lead, they will have to have speed 30 MPH higher than you to run you down in 1/4. Don't quote me on the exact numbers but you get the idea.