If your scene does not render at 60 fps then enabling sync in the cluster application will lower the framerate because all machines will wait for the slowest one. If you don't enable sync some of the machines may run faster but then they will be out of sync. To keep all screens in sync and maintain a high framerate you'll need to reduce the complexity of your models or optimize them. Here are some articles that maybe helpful:
Drawable Budget
Polygon Budget
Texture Budget
GPU Budget Intro