Don't forget the Evasionist's Cape also adds an extra -3% to physical damage and fits on par with the stats of emp jse accessories.
*** Edit 8-11-2013***
But if your looking for more -pdt with artifact then so far from what I can see or know of, the parts to add in are:
Twilight Torque -5%
Flume belt -4% converts 2% to mp (A must have for Rune when you think about it)
Evasionist's Cape -3%
Rune Af hands and feet -5% (both pieces together)
* Dark Rings x2 1%~6% (thats a max of -12% pdt if your lucky and you might get a decent second or third augment also)
**Jelly ring -5% pdt +5% Mdmg.
I don't want to add in earings unless they exist or do alot of gear swapping except for maybe weaponskills. buit with the best stats on rings, thats a total of about -29% pdt. I don't know if it can get any higher for rune but so far thats actualy not bad considering how hard the mobs can hit in Adoulin. There's the boots from Peacekeepers for an extra +3% (-32%) , however I'd replace them with Rune's Af feet once they are farmed/purchased.
*Because the stats are random you'll need to luck out at least on a -5% pdt or have a good second stat like Spell Interruption Rate reduction or more Magic damage reduction.
**Only used at low levels untill decent dark rings can be farmed.