Official Doppelganger is +10%...
The lower your aspd, the more effect a Doppel has. How?, you may ask. I'll show you. The formula for attack speed is 50/(200-aspd) It runs a standard 50 FPS, as opposed to the American standard of 60 FPS because it was developed in Asia. That's why the 50. So the formula for max attack speed is:
50/(200-190)=5 attacks per second.
At 181 there are 19 frames between attacks. So adding a Doppel into it, the formula becomes 50/([200-aspd].66) for one doppel, and 50/([200-aspd].33) for 2. Let's plug your aspd into both of these. 50/([200-181].66)=3.125 Attacks per second, or an actual of 184 displayed on your aspd. With two doppels, it becomes 3.846 Attacks per second, or 187.