kilgourd :
Bakua :
You definitely wouldn't need 3x 980Ti's for gaming, and even 1 GTX 1080 is overkill for gaming (unless at 4k, just note that not all games take advantage of SLI). The 2x 1080 would be the better choice overall, though, less power needed and less heat is produced.
It would be a 3 monitor set up at 1080p either 24" or 27" screens would that make a difference?
The screen size really wouldn't make much of the difference, the resolution does (eh, pretty much). One 1080 would be able to handle all of that, they're only 1080p (unless you're running different games that all require tons of resources). If you plan on playing one game with all three monitors, the 1080 would be great for that alone.