When graphic settings don't seem to matter, the next thing to look at is the CPU. SOMETHING is probably taking your CPU over.
If possible, tell one of your games to run in windowed mode. Before starting the game, start up Task Manager (control-shift-ESC will start it), tell it to show full details, then click on the top of the CPU column to sort all the processes by CPU. Put it off on the left side of the screen then start your game up in windowed mode and keep it to the right. When your framerate does its swan dive of doom, glance over at Task Manager and see if something is burning up all the CPU time.
There's a column for GPU, too. Some programs (like BOINC) will use that and it would have a similar effect.
P.S. If you happen to have two+ screens, you don't need to worry about windowed mode.