I'm not sure what ilevel is necessary for Durumu now (687 may be enough), but your armory has a number of issues.
- Mastery is terrible for DPS regardless of talent choice, and you're specced into Breath of Sindragosa, so you absolutely need MS enchants/gems - it's better than any stat at your gear level for DPS including strength and bonus armor. DPS legendary ring is also better with BoS.
- In 6.2 Breath of Sindragosa generally requires more multistrike than what you have to be used well but I find that it beats Defile on pure single target (Durumu) with ~15% uptime. Thus it would be better for Durumu given the fight length but not necessarily better for Garrosh.
- Glyph of Vampiric Blood is awful; forget that it exists.
- Pillar of the Earth is terrible - a 630 Toria's Unseeing Eye or Fires of the Sun would be better than that.
As for Garrosh heroic, I'm not sure why you'd hit the enrage - I guess you can use the tactic Mione did for normal mode? IIRC that reduces the DPS check, but it shouldn't be an issue at your ilevel.