There can be a number of factors causing your sketch to perform poorly. Some can be system or driver related. More often performance is affected by the data set you are using. Do you have a model with the poorly performing 3D sketch? Ideally, it should be saved in an earlier version of SW 2012 or 2013. That way we can eliminate systems issues and focus on the dat
You say that this was reported during Beta 2014. Do you have an SR number for this issue?
R&D SolidWorks, Modeling, Development Senior Manager