Multiple Graphics Card Question?

I’m in the process of deciding on a configuration for a new computer and I need some guidance on the best graphic card setup.

I need to be able to work with two monitors as well as getting the best render speeds in cycles for arch viz type scenes.
I’ve read through many threads and benchmark results and I am as confused now as when I started.

Should I buy a single card like a nvidia gt770 ti or go for 2 x nvidia gt750 cards?
If I get two cards will both be used at render time or does one stay dedicated to the second monitor?
If I get two cards is it possible/easy to have both cards contribute to rendering, for example is it as simple as turning one monitor off at rendering time?

My questions probably show the limited understanding I have about this so any help would be appreciated given the investment I make in this new computer needs to last me for some time into the future.

Hi, if you have one card the system is blocked during rendering, Cyles use nearly 100% of the card.
If you have two cards it is easy to switch one for Cycles off during setup your scene and materials/lightning.
For final rendering switch both on with one click.
The GTX 750Ti is the best bang for bug but it has only 2 GB VRam, have a look to your work files how many Ram you need on CPU for Cycles mostly.
I bought the GTX 760 4 GB because I don´t like to get out of memory on bigger scenes.
The GTX 770Ti is not as fast as it should be, dunno why, it is not faster than a GTX 760.
Here are the last benchmark numbers:

Cheers, mib

Thanks for the advice.