It is 56 from the front but many tanks settle for the 26 dps softcap. This will still effectively prevent the amount of times you get parried and dodged. In my informal research at expertise 26, I would estimate you still get dodged and parried about 3 to 5% overall. Of course any mood swings by the RNG can still throw that out the window.
That's not entirely accurate. Bosses have a 6.5% chance to dodge your attacks and 14% chance to parry your attacks. At 26 expertise you will fully negate the boss' chances to dodge, but you'll still have a chance to be parried. So at 26 expertise you cannot be dodged (by a 83 mob), regardless of mood or RNG, but you will still get parried. Which is why after 26 expertise, the value of expertise is considerably lower.
I've gotten some upgrades, but my threat still sucks HUGE vs Druids/ paladins / warriors.
Im now at 238 hit ( 7.26% ) so still not completely capped... Is it worth a 20 hit gem to loose 30 stam gem ?
Yes. Missing a single taunt or initial attack can severely mess with controlling fights (think if you miss a taunt on Thorim, for example). I would put it in your shoulders or belt though, since you're not using those socket bonuses anyways. Alternately, see if you (still) have Signet of the Impregnable Fortress to substitute for the Platinum Band of the Aesir. You trade some avoidance for the hit rating and can see how that works, with a much smaller loss in stamina.
For threat, assuming you're macro'ing Rune Strike, remember these things:
Paladin threat is nuts. Odds are, once they have it, taunting is your only way to take it off them.
Rune Strike requires RP to function. A common issue issue is folks dumping all the RP they can into Frost Strike or Death Coil, and starving Rune Strike from ever going off. Be sure to keep 20+ RP saved at all time, as an unused FS/DC isn't going to make the threat potential of RS.