Just throwing this out there. I know most socketing is based on individual toons and what each toon needs. But I wanted to see what people thought about socketing pure strength gems in a DK tank. I know strength is a no brainer for DPS. But is it possibly more (or at least nearly equally) beneficial to put in a strength gem instead of a dodge gem?
Increased threat generation with a slight increase in parry sounds good, especially when you want some more threat generation. A purple strength/stam gem would cover all 3 tanking priorities... health, avoidance, and threat generation.
So a Bold Scarlet Ruby would give 16 Strength which is 32 AP. It would also give 4 Parry Rating based on the 25% of Strength conversion. 4 Parry Rating converts to 0.08% chance to parry.
A Subtle Scarlet Ruby would give 16 Dodge, which converts to 0.41% chance to dodge.
Looking at this you're getting 32 AP (not sure how that coverts over into threat) to help generate threat, plus 1/5 of the avoidance of the dodge gem.
Looks pretty clear cut but I still want to get some thoughts anyway.
If you want threat go for hit or expertise, if you want avoidance go for the dodge. Your thinking on how much parry you get is supremely flawed, due to diminishing returns and a DKs natural parry from FD you're probably barely going to get half of what you listed.
Parry with BB on a dk is a horrible stat due to DR. Generally you should socket red = dodge/stam, blue = dodge/stam, yellow = def/stam for a DK. Dks are avoidence tanks but this choice will still allow for a nice EH build up.