Would having a second monitor decrease my fps in games? How exactly does that work? If I have one game running fullscreen on one monitor, does my mouse go over to the other monitor on windows desktop or something?
I haven't noticed any impact on performance with my dual setup. Which is a 1080p main monitor and a 1280x1024 side one.
If you play fullscreen mode, mouse is locked to the monitor the game is on. If you play fullscreen windowed mode then the mouse will go over to the other screen. Depending on the game, if that region scrolls the map it can force the map to be stuck scrolling until you click it off focus. IE EUIV will scroll until another window gets focus at which point the game minimizes.
There is a performance difference (albiet not all that great) between fullscreen and fullscreen windowed mode.