Well I'm no expert here but it seems that DFI may have lost their way a bit recently have a look at the video feeds in this mag by what I consider are a lot more experienced OC's than me, most think that DFI has lost something lately (makes me think of Crucial);
The Overclocker: the world's overclocking magazine : The Overclocker magazine
You could also look at SKYs' review on the 4870x2 and DFI:
Palit Radeon HD 4870 X2 2GB Video Card Review
Things aren't looking the best for DFI at the moment.