Okay, so, I've used Doublade on my stall team for a while, and here's what I have to say:
1. Doublade can never afford to stay in on a Bisharp. Ever. There is therefore absolutely no point in running Sacred Sword
2. Specially defensive Doublade can sponge just about everything that isn't supereffective against it, which is good. It rarely can hit back, however
3. If the opponent's Mega Heracross hits a Doublade switch-in with a Pin Missilt or a Close Combat, a switch follows almost always, as most Heracross, indeed, no longer run EQ. This makes Aerial Ace almost as moot as Sacred Sword. The only attacks I have found myself using were Shadow Sneak and Gyro Ball, plus, I used Toxic, like, twice in ~30 matches. Doublade usually acts like a wish-receiving universal sponge for hits (resistance to SR helps to take the pressure off if my back if I fail to keep hazards off the field), or, simply said, as a Close Combat-immune pivot switch
So, I use this set:
Doublade @ Eviolite
Ability: No Guard
EVs: 252 HP / 4 Def / 252 SpD
Sassy Nature
IVs: 0 Spe
- Aerial Ace
- Gyro Ball
- Toxic
- Shadow Sneak
I'm thinking that there might be some merit to running Swords Dance after all (instead of Aerial Ace), just so that Shadow Sneaks do 30-35% instead of 18-20% (not that it itself is particularly useful - the only thing I can think of off the top of my head that this could help against is Swords Dance Talonflame...if it decides not to run Flare Blitz)