Not sure what the problem is, here's what I would look at first:
Make sure in the AMD control panel that Crossfire is enabled.
Make sure the ribbon connector is connected between both cards
To further verify, download a program called GPU-z and run it. It will indicate if crossfire is enabled.
As suggested, check to see if vsync is on, if it is, disable it.
If that still made no difference, I would get weird on it: I would downclock the hell out the cards (like down to 400mhz core speed) and then run games with and without crossfire enabled. If that lets you see a difference between crossfire and not, then there is something forcing vsync on your system.