Won't sleep status still interrupt cast time/effect? Or is GD unique in that the effect will go off whether or not the caster is stunned/sleeped/etc?
I don't think being slept cancels your cast (could be wrong), but you will be taking damage so quickly sleep shouldn't be an issue, and, while your build is for GC, a frontline GD Paladin would be:
90 AGI (base)
99 DEX (base)
Rest in anything except VIT
Using stun immune gears (Double Stala Golem + Valk Armor + Mega Resist or Gemini Stala Golem Valk).
So you'd be pretty near to instant anyways. And the constant MS/SG damage, Arrow Shower, FAS, Bomb, etc, would keep you from Sleeping for more than a few frames.