On the Tornado we run fairly high rig tension, especially in lighter air. The reason is that you want to keep the forestay from being too slack, which hurts jib & pointing performance going to weather. In the light, the main stay ligtly sheeted, so there's not much left to pull on the forestay.

We use a Loos gauge and typically run 25-30 on the new black gauge (pretty near the high end for 3.5mm rigging).