I play just one save, too, but I have not yet noticed any sim being culled. I have unlimited amount of sims though. I started with a limit of 200 (?), and now I have about 400 actively played sims. My experience is that the game performance was not very much affected by the population growth. But this might depend on whether the added population is in different worlds, because I do notice extreme lag in larger households and bigger builds. In smaller households everything works well, I might just need the game to load all aspects of the household/hood meaning it might be laggy for the first sim hour or so. I added tons of CC over the past couple years, and I blame most of my lagging on those, especially in periods when my hard drive gets filled up - doing a major clean up often helps a bit ;)
