GFX Cards and their attached monitors

Hi there - great YouTube channel by the way!

I have been running a set up for a couple of years now, which includes 4 monitors and 2 GFX cards. The primary card, a 1080, is running just my main monitor (ROG 144Hz 1440p and GSYNC), and the second card, a 780, is running the other 3 monitors which are just for work etc.

It's always worked fine and I don't have any problems per se, but is this the correct way to do what I'm doing? Do I even need the second card? I always though I did because I like to take advantage of GSYNC on the 144Hz panel and reserve all the 1080 horses just for that panel. But does software/hardware take over and do what it wants anyway?

It's a i7-4930k so PCIE lanes are a plenty I believe.