If you go Fatesinger (or other arcane ED) you'll have +5 caster lvls, so eventually Haste will last 2m06s.
I can't crunch the DPS math myself, but my hunch is +20% offhand from GTWF is worth more than OC; more so if you go for Shadowdancer ED, since the more offhand procs the more sneak atks you'll make. So if you drop anything, it should be CL/GC/OC, IMHO; beef up your metamagics instead.