v40b is just that, a Beta, so i have also run into the same problem but only with certain games. I would suggest you try Azimers v0.30 (old driver) as i use it and only have 2-3 games that have any stutter at all. I dont know your system specs, so that can also be a factor, hopefully you have a 850 mhz or better (like a 1.0 ghz+), as the lower your mhz, the more things will stutter and the lower the framerates.