That depends on the game. So it can't be calculated, but only benchmarked. So just do it and see the result. I don't think the monitor makes a difference, so just using 3 of your current monitors would suffice.
I want to play games on three screen at 1080p
Can anybody calculate my average fps.
NVIDIA GeForche 1080 TI founders edition
The monitors I am planning to use are the Samsung CFG70 27 Inch