You can probably get away with moving it now in your zone. I've done it with no ill effects. If the fall is normal, there are still several weeks before hard frosts.

Cut the plant back to 1/3 its current size.

Prepare the new planting site by digging a hole twice the size of the rootball. Leave the soil you've dug in a circle around the new hole. Loosen the soil at the bottom and sides of the new hole, but don't amend the fill soil, unless it is too rich for Panicum, in which case, cut it with poorer soil.

Cut the rootball about 3" out from the crown, at least 12" deep and at a slight angle inward.

Once you've circled the rootball, you should be able to rock it out with little root damage.

Soak the new hole with water, and soak the rootball (gently), and install the plant with the top of the crown at the same level as it was in its original site.

Use the soil ringing the new hole to backfill around the rootball. Fill it 1/3 the way, tamp and water. Continue until the new hole is completely backfilled.

Water thoroughly every couple of days through the fall, unless there is sufficient rainfall.

donn - Cut the rootball about 3" out from the crown? Inches, really? Woo-hoo! I'm a happy gardener. Thanks.