A single pass through a 6.5 STW Full length die will propperly neck down the cartridge. As for Die Choices, I really like Redding as a first choice, RCBS as a Second choice and Hornady as a third. More than likely the only one of the three that carries that die ready made and on the shelf will be RCBS. You'll probablly have to wait to have it made by Redding or Hornady and you'll expect to pay upwards of $150.00 for the set. That's not including a Benchrest or Micrometer seater or a Bushing style die, just the standard set.
Dan