Cod4 run better at dual then quad? why do you said so? any SOS?

Anyway , i got a question wondering in my mind since the day i bought my PC.

Im a AMD/ATI Fan User .

So i bought this Asus HD 4870 512MB DDR5.

I just want to know , all this brand like Asus / Gigabyte / HIS / Sapphire they

don't really make a difference right? its just the brand name. Because i googled

and the specs almost all the same..so is the review.

Any pro here might tell me whats the real diff actually?