You cannot compare Intel and AMD clock-for-clock. Intel's CPU's are now about 30% to 50% faster, clock-for-clock. If you price compare. You will find you are paying more for an AMD that performs the same as the Intel, and for more money, you can simply run away from AMD. For example, AMD has nothing, performance wise, to compete agains the Intel E8500 no matter what the price.
Quad core CPU's are a bit of a waste, unless you are doing real time video and/or audio encoding. Those are the major reasons for quad core, and there are a couple of other applications that could get 15% to 25% better performance from a quad core CPU, but for the price, the dual core CPU's offer far more band-for-the-buck to the general user. If you go top end, the dual core will simply blow away a quad core CPU in raw performance in most applications.