Since curing is the White Mage's primary duty, gear to increase potency will always be the top priority. Ignore the cries of 'only 2%!' because the reality is that it is a 20% increase over NQ
Until you get the AF3 body with Afflatus Solace buff for single target healing this is one of the best healing coats. Let's say you're a level 75 WHM and you have a total of 50 MND, 30 VIT, 300 Healing Skill, and 25% Cure Potency. 10% Cure Potency from the NQ will boost your Cure V by an additional 65 HP healed, while 12% Cure Potency will boost your Cure V by an additional 78 HP healed. That's 13 extra HP healed than from the NQ. It may not sound like much, but to do the same amount of extra healing you'd need to get either another 23 Healing Skill or another 46 MND. It's also quite nice for aoe heals since Afflatus Solace only affects single targets using single target cures.
As of Sept 8, 2010 update, WHM can easily cap out on cure potency without this piece. It will likely become even less necessary when the level 99 cap comes around.
10% Orison Cap +2
20% Surya's Staff +1 (20%)
12% Aristocrat's Coat
3% Fylgja Torque +1 or Orison Cape
5% Roundel Earring
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50% with big MND slots like rings free
10% Orison Cap +2
20% Surya's Staff +1 (20%)
10% Noble's Tunic
10% Medicine Ring or Serpentes Set
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50% a lot cheaper
Roundel Earring (5%) and ASA legs (5%) could also replace the Medicine Ring, but Orison Pantaloons +1 are a better option for the leg slot if you can get them.
All I have to say to people about paying "too much" for HQ gear like this... pay more for NQ and the crafters won't have to sell the HQ so high. That's right, Economics. eat it.