The only exception is the flexibility the X6800 gives you since the multis are unlocked.
So overclocking/underclocking (1:1 if needed) is easier on the X6800.
Now if you are asking if an E6600 OC'd to 3.2Ghz is as fast as an X6800 @ stock then I would have to agree.. They would be very close. This is the reason people have purchased the E6600... An OC to 3.2 is not difficult either.