should be mentioned here i think. Both as a factor they exist, and as covering they functionality.
http://www.pcgamingwiki.com/wiki/Topic:Y37v890xufgfqril
Also i want to mention here that while default and GOG/EA defaults conf-files are good as is, there is something need to adjust. As default, as mandatory. Cycles gradation by Shift+F11/12 (or which one?) too large. Sometimes it did need adjust during game from default "Auto" (X-com speed not the same as on WIN) and not so useful with default gradation.
Also maybe default resolution, screensize and full/window screen are subject to changes? Not sure about this ones. As i remember there is Keep ratio enabled by default and else settings are good as is.