It could depend on the custom JS code that is executed in the callbacks. We haven't seen any performance issue on IE with our samples (only the optional fading effect is heavy, but not blocking). Can you please explain us how to reproduce the problem?

In any case, there is a heuristic mechanism in our client library, so that if the code detects that the browser is not able to keep the pace of the inbound updates, it automatically switch to smart polling, in order to find the right pace. In this case, the server-side throttling, conflation, and batching algorithm will take place, in order to provide the best user's experience given the supported client-side frequency.