Ideally I'd be able to construct queries and then save them under a name, sort of like bookmarking a site. Pretty isn't necessary. Fast is preferred. I'm open to client solutions like Access or FileMaker. PC or Mac would be fine. If online, I'm open to a PHP script, like maybe ezSQL or Appgini. Dedicating web server to this is fine too, as is using Amazon.
Main question is whether the tool can handle 50 million records efficiently.