It all depends on weight of the sled and the bite of the track. Some little sleds, pull back sleds, 40,000 lbs or so, you might be alright. Big sled like a powered return sled weigh anywhere from 75,000 - 100,000lbs can burn a stock clutch!! Better to get on down in the lineup and watch the other guys. Seen many a clutch get burn up due to too high of a gear. It is really hard to answer without knowing the sled, track, rpm capablitlity of the pull truck, horsepower, clutch, etc...
To make it short and sweet, you want as much wheel speed as possible after getting the thing rolling, yet not fail on your face at the end. You need to be able to carry you wheel speed through the duration. Recommended to be able to spin out at the end. You tires are spinning you should be alright. No tire spin means something else is going too or you'll just lug out at the end!!
Sleds are a good ego check for driver and truck alike. You'll have a new appreciation for heavy if you hook to a big sled!!
Watch out! "Once you hook, your hooked!" Very addicting sport!