Nadagast + fan:
1537 int (including OH-enchant, plus socket-bonus)
843 spirit (470 hit)
1 gem slot
Invocation of the Dawn:
Nadagast + fan gives ~1000 SP more than 2h, so I'd go with that.
I'd say so, yeah. The loss of crit is pretty much non-existant seeing as the gemslot is yellow and you get a 320 crit gem. You'd only lose some mastery, but gain some haste and spirit which can be reforged. So I'd definitely go with 1h+OH.