No you wont. I run 4 monitors. (EyeFinity + 1). Having the extra monitors on during gaming doesnt effect performance unless you have something running on the monitors that is trying to use GPU power. Most of the time when gaming I run EyeFinity so am gaming on 3 monitors and can still have applications (tv, video playing, system monitoring software) on the 4th. The only time I've taken a hit is if whatever I'm doing on the 4th screen tries to use the GPU. I've found running Windows media Center or flash video in a browser use GPU acceleration so they will affect play or even stop the GPU from going up to full speed (stays in low power mode since it detects that the flash video doesnt need much power).