Try editing the Engine.ini file in the My Documents/My Game/BioShock Infinite/Config folder and change the Min + MaxSmoothFramerate to 59 and 61 respectively plus change the two MemoryPools variables from 512 to 1024. That significantly reduced the stuttering for me (unless it is coincidental?) but the game does still hitch from time to time, usually when entering a new area or when VRAM gets close to 2 GB. It was really bad before though so any improvement is welcome. I'm playing on maxed out Ultra 1920x1200 settings by the way with Alternate post-processing.