Latency
The Infinity Engine games were originally designed to be played on a LAN, but changes that were made in the 2.0 versions allowed for improved connectivity on the internet.
A maximum latency of 100ms will provide a good gaming experience. Any clients with a higher value than 100ms will notice issues in the game such as stuttering game play, hitching, and other delays during the session for all clients.
For the most part, there is little that can be done to improve latency between two clients, aside from upgrading/improving your internet connection or moving physically closer.