Not to compare this game to any other but.... I get pretty decent framerates in Arma 2 w/ ACE mod very high settings, which is a resource hog with all the things going on in large sized battle with tons of AI. Likewise in CMBN i stay clear of large battles cause the fps drop is too much to handle, but generally I'm content with where performance is now.
Having got CMBN an seeing the performance increases over time I now cant really stand to go back an play CMSF anymore. Its mostly graphical issues but I do notice its more sluggish an really spoils the experience. I guess that just goes to show BFC is going to continue perfect the engine overtime.