OP, below are my tests with my e8400/GTX460. The point is that while you'll be able to crank graphics quality in crossfire, you'll never be able to exceed the FPS of any of the games in that techreport article tested at the lowest resolution. That is your cap, and for many new games like those tested, the cap on a dual core at 3.4 is pretty low.
This is in BC2 with my e8400@3.3 and my GTX460@800/1000.
1680x1050/medium/1xAA/4xAF/HBAO off
Min Max Avg
31 53 42.017
1680x1050/high/4xAA/8xAF/HBAO on
Min Max Avg
32 56 42.75
1920x1080/high/4xAA/16xAF/HBAO on
Min Max Avg
34 55 42.767
I ran these two times, because I couldn't believe the results. I figured it was user error. Apparently it wasn't. This is all on the same level, same server, within a 5-minute span. You can see I'm completely CPU-limited.
Now, just because the above results are so hard to believe, here are some more examples on a different level/server.
1280x720/1xAA/4xAF/medium/HBAO off
Min Max Avg
31 55 43.733
1680x1050/1xAA/4xAF/medium/HBAO off
Min Max Avg
34 68 46.233 (yes, higher than at 1280)
1920x1200/8xAA/16xAF/high/HBAO on
Min Max Avg
26 57 37.183