Well, for the most part I think 2 screens is more of a status thing, than a necesity, unless you are a pro tools head.
It`s consuming more power, and also more oomph for your machine.

I`ll throw a spanner in the works and say one big ass will save you space, and a little bit of processing.
And you`ll be very comfortable with it.

2 screens really won`t speed up your working rate that much.