The 4870 X2 isn't "close/little better than a GTX 280", the 4870 X2 smokes it.
Eats it for lunch, Pwns it, rapes it, molests it, destroys it, need I go on?
The 4870 X2 Beats the GTX 280 in the vast majority of all the tests over all the reviews, thats not close...