As PR checking, WHOIS checking can also get you IP banned if you do mass query. With best WHOIS scrapper you can scrape up to 1 million domains per day and export you desired information including WHOIS contact, registrar, registering date, etc.
Best WHOIS scrapper integrated with keyword tools, gtld, cctlds. You can check the keyword domains availability with ease. It also powered with domain monitoring and email schedule features. You can be a domain master with it in hand.