Working with more than one monitor or keyboard

Can users work more efficiently (reacting faster, or, getting more information before taking a decision) with more than one monitor or one keyboard?

It seems to be a common practice among day traders to have 6x (or even more) monitors, and more than one keyboard. Specially having more than one keyboard seems to be a handicap. And since monitors got really big at a reasonable price, I see little use in having several of them. Maybe two would be useful. One for getting the information, another for whatever action one wants to perform.

There are surely other alternatives to deal with multiple sources of information. Knowing the appropriate shortcuts well is one of them.