Some registries support high speed domain availability lookups. These are are not rigorously monitored for high volume (ab)use. The downside is that these whois lookups are suitable only for domain availability checks.
You can configure all of our domain name management / search software tools to make use of the high speed availability lookups.
The above screen-shot shows the configuration required for AU domain lookups. Please remember to change these back to normal settings if you want to do regular whois settings. So, it is a good idea to note down the earlier settings before you make any changes.
You can adjust the ‘max connections’ and ‘connection interval’ so that the lookups occur at higher speeds.
The following articles explain the settings in more detail.