Collisions. The more things are colliding at once in-game, the less fps you're likely to get. Also grabbing and other things influence that.

Server lag is simply the time it takes for the packets of data containing information about what happened in each frame to get back to the client. That does not mean the Toribash client will wait until they're received to update the graphics, and as such, it has no effect on fps.

hmm ok good to know
the drivers are probably the problem but i remember how toribash was really slow for me due to my power settings
using pc wizard i found my ghz at half its factory setting