The system that I've used the FabFilter Pro-Q on is Pro Tools HD based. I don't know all the specs for the system that he's running, but it's an Apple G5 computer and Pro Tools HD, so not too many plug-ins are going to lag here. Even while this may take up more processing power than most EQ's out there, you still should be able to run a good amount of them once if you're currently able to run plug-ins without issues.
The FabFilter Pro-Q is probably my favorite EQ plug-in. It's just so in depth that it trumps most other EQ's out there based on flexibility alone. It also has a number of features like zero latency monitoring that you're just not going to find on most EQ's. However, the crystal clear sound of the Pro-Q makes it what it is. This is the perfect one stop shop for equalization and filtering, whether you're looking to remove a certain frequency or bring out certain colors in your sound. The price of the Pro-Q isn't too bad considering what you're getting here. If you're looking for something really cheap to get started with, the Micro plug-in is a one band EQ and is good place to start. If you're looking for a top of the line EQ, the FabFilter Pro-Q is the one I'd recommend.