Since day one performance was always important for Realtime.
In most cases Realtime will not take more than 5 milliseconds routing your messages. Unfortunately we cannot get around the laws of Physics, so the total round-trip-time from your clients to our servers will have a great impact on your overall latency.
If you want to get an idea of how Realtime performs in your current location checkout this on-line benchmark between several hosted messaging services: http://www.leggetter.co.uk/real-time-web-technologies-guide/realtime-hosted-service-latency/
Here's an example of the results you'll find: