On full/high pop official servers the infected are still quite laggy. For instance if they aggro on me and chase my character, every 3 seconds they will stop chasing me as if they lost track of me, even though I am only a few feet away. This makes it very easy to escape them. Other times they just get stuck on a fence or in a bush. In the past the infected were not laggy on low pop servers for me, but I haven't checked this on the new update.