+Spd Vs. -Spd Micaiah

+ spd - def, she shouldnt be taking physical damage

Micaiah hits 30 speed with a boon which will help her not get doubled, but in order for her to make use of her boon, she needs a lot of special investment. (I've had both a +atk-res and +spd-res, so this is just my personal opinion on her (she's +1 so my numbers may be 1 or 2 off here or there, keep that in mind))

I actually went ahead and built a speedy Micaiah and she preforms REALLY well. Mine has a 50/34 atk/spd spread with a spd3 seal, and to boost her doubling capacity I run her with darting blow, desperation and speed ploy (35 res is usually plenty to ploy). On PP she effectively has 45 speed if the enemy was properly ployed and with speed buffs you can up that number. Even if the ploy was unsuccessful, a basic hone/rally speed can get her to 44 speed. Add in drive speed on one or two support units and she'll double everything that matters. You could also sacrifice her defensive capabilities and run LnD for a 55/39 spread. At 35 res and a 30% damage reduction from ranged cavalry/armored from thani, she probably won't miss the -5/-5 def/res.

I'd definitely take speedy Micaich over a speed bane. You could probably get similar effects with a neutral speed stat, but I'd take the boon.