There is a white paper made available for planning your performance testing scenarios for K2. I think this is a valuable document that will help you understand the performance factors in relation to K2.
KB000401 – K2 blackpearl Performance Testing White Paper
In order to evaluate the performance of a K2 environment, guidance in this document can be used for customers to set up their own performance testing. Actual K2 performance can vary greatly across environments and scenarios due to variable hardware and network configurations, as well as the types of business solutions developed and technologies with which K2 blackpearl is integrated.
Also checkout this performance monitoring KB