You will still be capped if you currently have 550 defense. The Triumph trinket is by far better, in a pure physical fight where the 70 one would have the best change at defeating it in pure stats, it would be 162 stam worth of armor compared to 42 defense is no contest. And the Glyph's on use is much much better.
In the trinket slot I would also recommend the Black Heart, the only place where Lavanthor could stand a chance is pure physical in which if you include the proc the Black Heart is worth 220 stamina which is also no contest.
Forte cooldowns is a nice CD addon, I would also get a Sword and Board proc watcher since that is the real variable in a threat rotation. I am not sure there are any addons that show threat instead of health but Aloft has something very similar.
I would get the Glyph before you get the Leggings, the Leggings are an upgrade, but a small upgrade. The Glyph will most likely last you longer considering that the 25 man legs are a clear upgrade while Satrina's, Black Heart, Glyph combo can be swapped out fight to fight. Keep Ick's for Saurfang and Gunship though.
And for your spec I would definitely get rid of 3 points in Cruelty and get Deep Wounds, Deep Wounds will add much more to your damage output than Cruelty is.
I would go with the ring next, it is a HUGE upgrade compared to the crafted ring. And yeah your spec seems pretty decent, one thing I would change is max out Shield Spec and Improved Tclap but that isn't worth respeccing since that money is better used for enchants and gems. But if you do have some spare money I would make the change.