Chunk rendering/loading on any render distance affecting framerate or internal server stability when you begin loading any chunks within what is considered the "world spawn". Frame dips will occur, slashing fps by enough to see noticeable stuttering, or the game will freeze for up to about 8 seconds.

This may have to do with generation instabilities with pre-14w03a/b worlds only or something. As soon as I get out into 14w03b+ generated areas, the lag is completely gone.

Any stress on the system will make the game lag exponentially more (as expected). More mob spawning calculations per minute (i.e., higher render distance/MPChunkCache), more mobs within the loaded area, more lighting/redstone updates, higher render distance (includes on peaceful), higher graphics settings and faster movement/unloading and loading of chunks will all increase lag, stuttering and/or internal server stability issues in or around what is considered "spawn chunks".

Slightly less of a chance of this happening with more adequate hardware, but is prevalent to an extent regardless of system specs. Internal server instabilities creating "block lag" exists regardless of snapshot, area, etc. as long as chunks are being generated, but do not create frame stutter/drops at all as long as you are not rendering "spawn chunks". This is only noticeable when first generating said chunks as well. Mostly clarifying the type of "lag" I'm getting at or around my world spawns.