currently have 1 30' plugged into the dvi slot, and a 27' in one of the Display ports.
If i buy another 27' and use the second display port, would this cause problems? would it even work?
and also if it did work and i wanted to buy a 4th and 5th monitor and use the 2 HDMI ports would this alos work? or how bad would it effect PC performance?
Depends on what you are doing, IE gaming or poker or web stuff, on how the computer will perform. Also depends on the resolution of the monitors. Like three 4k ones and you're prolly not going to be happy.
Adding more display port monitors should be just fine. I'm not sure which card you have, but most have 3x DP, 1x HDMI and 1xDVI. You can use all 5 ports. Are your HDMI ports on the video card or the motherboard?
