As many of the people of above have said, what do you define as "bad frames"? This is extremely important as for me, and my typical frame rate I would say 26 frames would be bad frames. I'll assume when you say bad frames you mean un-playable so somewhere around 15 we'll say. First of all mods may heavily impact your performance, as well as things like fog which even with my beast PC it drops frames extremely bad. You might want to try messing around with certain settings as well. Anti-Aliasing is a setting that can sometimes have no regularly noticeable visual difference, but can do wonders for your frames.