If transferring 33,000 URs to Avios the opportunity cost is 33,000 * 1.25 cents, about $412.50. Add the $257 and the total for the ticket is now $669.50. Using 60,662 URs is costing you about $758 in opportunity cost, so I would transfer the URs to Avios in this instance. Although of course you would earn miles with the UR ticket it won’t be enough to make up the difference.