It looks to be far enough ahead that even with a lower ilvl offhand it'd still be slightly better. I was trying to think of a good key to use for the cancelaura, and that's a great idea to put it on charge.
I'm gonna try and see if there are breakpoints for DR/BS usage on 1 target, I could see lower crit levels being a concern, as bladestorm has been scaling from crit all expansion while DR has been capped. Also, ilevel discrepancy with gear and weapons, so if your average ilevel is 570 and are somehow still wielding 540 weapons, DR may be a better choice. It's likely that DR is still optimal for SMF, though.
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Yeah, these are extremely minor dps increases. IMO, the biggest gain for BS on IJ is that you don't have to worry about clipping a mine with DR.