Watchdogs stutters like a total biatch when using SLI, but can run very smoothly now on one card. This is widely known and I've extensively tested it too.
This is on 2 cards however, so unless running on 4 cards has some bizarre influence on stutter (I would think it would be worse!), I suspect your definition of smooth isn't the same as mine
There are rumours that downgrading to an earlier version of the game and using a specific driver sorts out SLI stutter, but I suspect it's nonsense as it's stuttered with SLI from day one, regardless of version or driver!