Upon modifying Minecraft I noticed, that fluids spreading (especially in caves) cause the majority of lag when generating new chunks. After some investigation I can say, that this is also true for Vanilla Minecraft. I also tried some mods, that remove waterfalls in caves entirely and was surprised to see, that there was barely any stuttering at all, not even noticeable when not looking at the TPS graph. The second biggest source of gen lag are leaves, which pale in comparison. I therefore strongly believe, that by improveing the behaviour of spreading fluids somehow (and also reduce the amount of obsidian forming) can provide a jitter free experience on even very high render distances. DAMN YOU BLOCKUPDATES!