Given that 3mm shrouds are rated to ~1200 lbs...that's gonna be about your max tension ;-)
If you're talking about how much tension you should set your boat up with...The tornado is setup with a 24-30 range using the newer Loos gauge. Not sure what that works out to in pounds.
The main idea is to create enough tension in the forestay to prevent the jib luff from bowing excessively when there's not much mainsheet load...such as in light air.
