Jeff:
To be sure, I'm never said that the surbl servers in particular are slow.
I was simply saying that because many more lookups are required per message when using SURBL (when compared to the traditional RBL model), much more reliability and speed in required of one's DNS server.
I suspect that all you pros out there participating in lists.surbl.org have such good Net/OS/Software/hardware setups that this was never a problem. ...but should someone come along and complain about SURBL lookups slowing them down and if they are using a Windows server, that software I mentioned will probably help.
Rob McEwen