If it's purely for threat purposes, you'll probably get a bigger TPS increase per point of Strength than Expertise or Hit Rating. That said, for an MT set I'm not big on gemming / enchanting for threat anyway - aside from possibly Hodir Hard Mode, you shouldn't have any trouble keeping aggro anyway, especially with a 3/3 Crusade build. Paladin threat is already crazy high so in my opinion your gems and enchants are better spent on EH and avoidance / defense rating.
In terms of your spec, the only thing I'd personally do is drop from 5/5 Conviction to 2/2 Vindication, 1/5 Conviction and 2/2 Persuit of Justice.
Gear-wise I really don't like the Wyrmguard Legplates myself, but they may be the best available to you so fair enough. The Tier 8.5 are awesome though so grab those if you can. You may also benefit from Mark of the Relentless over Signet of Winter due to the huge EH potential.
All this is quite nit-picky however. As I say, I'd personally move away from the Expertise and Hit and focus more on EH and avoidance, but you should be fine to tank any current content.