The first 3 mods all have different levels of quality configs to choose from when installing. CCC has 5. Some may even degrade visuals slightly but provide tremendous performance benefits. The TOD (time of Day) modifications that come with most of these will increase the quality of the visuals more than any config will, but at a performance cost.
But if you are having crashing or menu problems in DX10 then these mods can be particularly helpful. Using these configs and TOD mods you can run the game in DX9 without having to give up most of the features that come with using DX10, like god rays for example. However you will not be able to use object motion blur without running in DX10.
Relix Crysis is very GPU bound. That's why it isn't using very much of your CPU's power. BTW what are your PC's specs? I remember you upgrading recently.
EDIT: Sorry forgot the link to the the best site for Crysis mods.
http://www.crymod.com/portal.php