for right now all dual card setups can suffer from microstutter. with all combination of discrete, onboard or on-die GPUs. its only noticeable with lower frame rates and noticeing it is dependant on the person, as each person has different refresh speeds from their eyes to their brain. i personally notice it under 60fps but my brother doesnt notice it till its slows down to 35fps.
this wont be a problem in a couple of years as there is a new way to cache images before they get sent to the monitor but it takes time to implement. i was wishing that the radeon 7k series would implement the new buffering but no mention as of yet. they get "released" tomorrow.