This is my settings for Ultra settings at 1080p on a single card. You don't need super sampling to make it look good. Super sampling just bogs down the framerate, and it's pointless unless you have SLI.
GPU: Gigabyte GTX 770 4GB OC (1200/1800)
You need to download Sweet FX 1.5.1 Configuration
http://sweetfx.thelazy.net/
Download the Sweet FX Watchdogs preset. There are a few but I chose this.
http://sfx.thelazy.net/games/preset/1675/
Load the watchdogs.exe on the Sweet FX configurator. Then load the preset. Some people might have trouble viewing the preset, but close it, and reopen it.
Once you see the preset configuration, simply click add sweet fx on the right column then save config.
Use the Reddit PC tweak guide here
http://www.reddit.com/r/watch_dogs/comments/26c3ew/deferredfxqualityconsole/
DeferredFXQuality= PC
PostFXquality = off
Resolution= 1920 x 1080
(Adjust to your liking)
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After you are done with the settings, this is what you should have.
AA: OFF (Sweet FX has it's own SMAA)
AF: 16x (Through Nvidia Control Panel)
Ambient Occlusion: HBAO+ High
Shaders: High
Shadows: High
Everything else Ultra
You'll get at least around 45 AVG fps.