Currently at 347 STR and 191 DEX, focusing on getting ilevel 90 tank accessories and not the ilevel 70 crafted DPS ones, I parry 23% of a hit and I seem to parry about 22% of the time according to the same model you use.. If I dropped all my tank accessories (assuming all ilevel 90) I would sacrifice 25 VIT and 15 Parry (this includes melds into DPS accessories) to gain 2% more parry mit and roughly 5% increased parry chance which is basically .1% flat mitigation? I can see getting STR and some DPS stats for damage/enmity and self healing, but DEX seems like a giant waste of points just to increase the chance that you mitigate a % of a single hit at least Parry just inherently comes on tanking gear. I highly doubt that full ilevel 70 crafted accessories melded for tanking will net the same effective HP a tank has with pure tank gear.

If you just look at the 25 VIT alone, the DPS accessory setup needs to equate to 6.104% more mitigation just to equalize the loss in the VIT, as far as effective HP goes. Obviously that isn't coming from the Parry boosts, not sure on the self heals, that could use some testing.