Dresdner Kleinwort Wasserstein remains upbeat about mining companies and the outlook for the price of metals medium term. It insists high prices being paid for the likes of copper and zinc can be sustained despite others suggesting they have peaked. DKW has raised the world's biggest miner, BHP Billiton - ½p better at 708p - from neutral to overweight, while upgrading Rio Tinto, up 9p at 1696p, from neutral to buy.