Legit Reviews carries on benchmarking the systems, testing a bundle of new games with various settings.  Drop by to get a feel for the best SLI and CrossFire can offer.
“Now, on to our experiences with the hardware. First and foremost I can’t help but be impressed at just how easy to set up and well mannered the SLI systems are. You just pop in the cards, install the driver, click the balloon to enable SLI and you’re off and running. While CrossFire is an extremely competitive platform it is still not to the level of SLI in user friendliness.”