to quote Anandtech again
"DDR3 at introduction is saddled with pretty dismal memory timings. As you can see in our test bed chart, SPD timings are 6-6-6-15 at DDR3-800, 7-7-7-20 at DDR3-1066 and 9-9-9-25 at DDR3-1333. "
http://www.anandtech.com/memory/showdoc.aspx?i=2989&p=8
Good DDR2 beats that & at considerably less cost.
Again, everybody agrees that once DDR3 improves in speed & timings that it will perform better than DDR2 but that isn't now (heck, you can't even buy DDR3 atm) or in the short term.