It's 3Gb/sec per lane. Keep in mind there may be other bandwidth limitations. For example, if that card is PCI, you're going to be limited to 133MB/sec for the PCI bus. That's a whopping 1Gb/sec or so. So your controller might be wicked fast, but other bottlenecks may be a serious problem. So as the admin for your server, as you design and build it, it's important to know all of the different speeds and potential bottlenecks. Otherwise you'll get it build and then kick yourself when it performs like a dog.