This will ultimately be up to the user expectations. Latency that is below 50ms is considered excellent. Latency below 100ms is considered good and latency below 150ms is usually considered acceptable. Slow latency does not mean that ProjectWise will not work but does mean the users perception will be that it is slow. Latency numbers of 300ms+ are common when working in a global collaboration. There are many things that can be done to minimize the effects of latency on the ProjectWise Explorer client.