links? As I remember it, most of the issues were around the fixed frame rates that were an attempt to unify PC development with console development. Perhaps I am confusing Doom 3 for another game though.
"Carmack has also admitted that the flashlight was not attached to the weapons in the original version of Doom 3 due to performance issues" ... http://www.dsogaming.com/news/john-carmack-speaks-30fps-on-c...